Tetsusaiga (鉄砕牙 Tessaiga ) is a fictional sword in the anime and manga series InuYasha, wielded by half-human, half-yōkai (hanyō) InuYasha. The kanji, directly translated, means "iron-crushing fang".
The Tetsusaiga was made from a fang of InuYasha's and Sesshomaru's full-blooded yōkai father. In its "docile" form, the sword looks like an ordinary (and rather battered) katana. The sword is enchanted with a barrier that severely burns any full blooded yōkai who might try to wield it, and will not transform at all unless the wielder has the desire to protect humans (though this requirement is only seen once). In its active state, it transforms into an incredibly large and heavy weapon that somewhat resembles a cross between a traditional zanbato and a falchion. In this form the tsuba (handguard) changes into fur and the rest of blade resembles a very sharp fang. This fur is supposed to be white, similar to Sesshomaru's mokomoko, since it comes from their father who had silverish white fur. In the anime, however, the coloring for it is inconsistent, sometimes white and sometimes brown. Since Tetsusaiga is a sword designed to protect humans, its attacks are extremely deadly to yōkai in particular. It is said that the Tetsusaiga has the power to slay 100 yōkai in one swing by striking using the Wind Scar technique. One notable example of this ability was the effects of the Wind Scar on Sesshomaru, who has shown incredible resistance towards holy and divine attacks, yet was injured severely by the Wind Scar. Furthermore, Tetsusaiga's Bakuryuha technique can only be performed on a yōkai or something with youki energy. Thus, it can be concluded that Tetsusaiga was created to specifically kill yōkai. Non-yōkai with unusual powers, such as Kikyo or some holy men, can sometimes neutralize the sword or its attacks.
Upon InuYasha's father's death, Myoga acted upon his lord's final instructions and hid Tetsusaiga within the tomb of InuYasha's father. The gateway to the tomb was then hidden inside a black pearl that was somehow cast into InuYasha's eye without his knowledge. Upon receiving Tenseiga after his father's death, Sesshomaru began to seek out the Tetsusaiga, and was enraged to discover that it was enchanted against his ability to master it. He has wielded the Tetsusaiga in brief moments, but the barrier around Tetsusaiga rejects him, severely burning his flesh. It is obvious that InuYasha's father intended this from the beginning, so that the brothers could not duel to the death after he was gone: Tenseiga could not kill the living until Tōtōsai reforged it, and it has protected Sesshomaru from the blows of Tetsusaiga on occasion, although he was still weakened considerably for a time, most likely due to it not protecting him until after he'd already been hit by the brute force of the attack. Tetsusaiga's sheath similarly protects InuYasha from attacks by other yōkai swords.
In a confrontation with Goshinki, an incarnation of Naraku, the Tetsusaiga was broken in half. The sword's creator Tōtōsai was able to repair the Tetsusaiga using one of InuYasha's fangs. The result is that Tetsusaiga now became dependent on the strength of InuYasha himself, as opposed to his father's, making the weapon heavier in battle and more difficult for InuYasha to wield because Inuyasha is much weaker than his father. Tōtōsai told him he would have to equal or exceed his father in order to make the sword lighter. After much training and a battle with the yōkai Ryūkotsusei (whom InuYasha's father battled to a standstill shortly before his death), InuYasha learned how to use a greater power created from the convergence of the Kaze no Kizu(Wind Scar) and attacks from a powerful opponent, known as Backlash Wave (Bakuryuha).
Tetsusaiga can also absorb magical abilities by overpowering and cutting into a creature or object that possesses them, for example; barrier shattering (from Shiori's barrier orb) and Kongōsōha (Adamant Barrage, from Hosenki (Hōsenki). It is however, interesting to note that he has not ever obtained an upgrade in the fashion that he expected to. The power has only been able to be absorbed after InuYasha has shown some sort of emotional maturity, morality or personal growth. The afore stated growth seems to have some sort of unexplained effect on Inuyasha's power (his desire to protect someone close to him is a major underlying factor in all of these instances, such as transforming Tetsusaiga for the first time or obtaining the Kongosouha attack). When Tetsusaiga became heavy, he ended up losing it when he fought with Ryūkotsusei. He transformed to his full yōkai form, and started beating Ryūkotsusei but after being smashed into a cliff, Inuyasha remembered his promise to Kagome and the deadly power of this form, which allowed him to pick up Tetsusaiga.. Upon taking hold of the sword, it became feather-light to him and he was able to use the Kaze no Kizu anytime, as well as discovering the Bakuryuha. When he attempted to cut the barrier orb, he could not cut it due to a barrier around the orb. However, when he felt compassion for Shiori and protected her from the orb's power, he was able to obtain the orb's power without ever having cut it. The same thing happened with Hosenki. When he attempted to cut Hosenki, he didn't even seem to scratch him, and instead ended up being peppered with diamond shrapnel that stuck in the wounds like glass. However, he abandoned his attempt to cut Hosenki when he saw that his friends were in danger, and consequently was able to use the Kongosouha technique. A simplified explanation of this is provided by Inuyasha himself, who states that Tetsusaiga has the ability to absorb the powers of enemies that it cuts.
In a final battle with Kanna, most of Tetsusaiga's powers were temporarily stolen by her mirror yōkai, who used these powers against InuYasha's party with a conjured replica of the sword. However, he compensated by using his connection to the real sword to empower it with his own innate yōkai power. After Kanna's death, Sesshomaru received fragments of her mirror, ground them into powder and sprinkled them onto Tenseiga. He then proceeded to steal Tetsusaiga's powers as Kanna did, and during the resulting confrontation, Tetsusaiga absorbed the Meidou Zangetsuha technique, and it a was revealed that while in Dragon Scale form, Inuyasha can use Tetsusaiga to cut his own yoketsu and exponentially increase its size, and thus his own power.
Kenatsu (Sword pressure) is when Tetsusaiga, like Tōkijin, and most swords of demon origin, has the ability to cut an enemy without making physical contact. It was used by Sesshomaru in Episode 18 of the anime. It has the power to slay 100 demons. It was also used by Inuyasha in Episode 28. InuYasha can be seen using this ability before he discovers Tetsusaiga's top-end Kenatsu: Kaze no Kizu, the Wind Scar.
Kaze no kizuEdit
Kaze no Kizu (風の傷 Scar of the Wind or "Wind Scar" in English dub) is a special attack technique that can, like the kenatsu, kill 100 demons with a single stroke. The technique is the base attack of the Tetsusaiga. This attack is accomplished by finding the fissure or scar between colliding demonic winds of Tetsusaiga's wielder and the opposing demon. Once the wind scar is found, the wielder of Tetsusaiga can swing the sword into the scar, which releases a powerful energy wave that has the strength to end 100 lives in one strike of the sword. InuYasha first used this attack by finding the location of the scar with his enhanced sense of smell, but eventually he learned to see the Wind Scar.
When the wielder becomes proficient enough, the Kaze no Kizu wraps itself around the sword; allowing the energy wave to be released at will, without a need for visualizing the scar between winds. After wounding Ryūkotsusei, InuYasha gains the ability to unleash this attack wherever and whenever he wants, without the need of finding the scar of opposing winds to cut. This was especially useful against Kagura, who could manipulate the demonic winds, preventing the Kaze no Kizu from forming. However, the user has to use his own demon energy to supply the power to form the Kaze no Kizu surrounding the blade. This explains why when InuYasha confronted Musō with multiple Kaze no Kizu, he could not keep it up forever as it would drain his demon energy. It also explains why the Kaze no Kizu manifests as a much stronger attack when used by the likes of Sesshomaru and the Inu no Taishou, as opposed to InuYasha. The strength of the blast also depends on how hard and fast the blade is swung.
Throughout the series he is shown to be mostly releasing lesser versions of this attack, using Tetsusaiga's Kenatsu. The only time he is using the full extent of its power is when he actually calls out its name.
Built upon this attack is the more powerful attack called Bakuryūha, also called the Backlash Wave.
Bakuryūha (爆流破, Explosive flowing wave, Crushing stream, Dragon twister in InuYasha: A Feudal Fairy Tale (PS): , Backlash wave in English dub) is the Tetsusaiga's ōgi (or ultimate technique). This only works on foes with a large demonic power. Uses the opponent's strong yōki and the Kaze no Kizu to return the attack, magnified hundreds of times. With this movement of the Tetsusaiga, he forms enormous charging twisters that sucks the foes power into the Wind Scar and forces it to flow backwards. The wind and the power twist together into a vortex, pushing it backwards and the enemy is attacked in its own demonic force and Tetsusaiga's might combined. But to use it, he must see where to cut the yōkai's aura and have strong enough ki himself to overpower his foes. InuYasha first used the ability in his battle with Ryūkotsusei, whom he killed using it.
During the first and second movies, InuYasha used the Bakuryūha to slay the "boss" villains, Menomaru and Kaguya, respectively. He used it multiple times in the third movie, ultimately combining the attack with Sesshomaru's Dragon Strike (performed this time by Tenseiga instead of Tōkijin) to send the living sword So'unga into Hell. In the fourth movie, he combines it with the Kongōsōha attack to create the Kongō-Bakuryūha (Diamond Explosive Flowing Wave) attack.
In the manga, it is used to destroy the gigantic bat yōkai Taigokumaru, and was used against the human swordsmith Toshuu, and his ryūjin sword Dakki/Datsuki, though it failed to destroy them.
In the anime only, InuYasha uses this attack to slay the dark priestess Tsubaki (who had merged with an ogre), Bankotsu (after he had powered up his sword Banryū and gained a powerful yōki attack), and the yōkai horse Entei (with help from Kirara), and Hoshiyomi (with help from Kagome).
Unlike other techniques in the series, Bakuryūha is the only one to be introduced in its Japanese name in the English dub of the anime; however, it is always later addressed as "Backlash Wave".
Sacred Backlash WaveEdit
This attack is actually a combined effort between InuYasha and Kagome. It consists of Kagome firing one of her Sacred Arrows into the center of InuYasha's Backlash Wave before it connects. When it hits the enemy there is a higher chance that he will be destroyed by the combined powers. Used in Episode 140 to obliterate Hoshiyomi and Movie 1 to kill the Hyoga.
In the video game InuYasha: Secret of the Divine Jewel, this technique is used (by InuYasha) to counter enemy attacks and can be used on weak-enemies (the enemy must attack InuYasha or a party member), as well as Bosses. The technique's only drawbacks (in the game) are its high energy cost (its energy cost is lower than the Wind Scar) and that it can only counter one (and hit one) enemy.
Barrier shatter (Red Tetsusaiga) is gained indirectly from the orb of the bat demons that gave them the power to create barriers. This technique renders barriers useless. Only the strongest barriers cannot be shattered by this attack, assumably it must be stronger then the barrier made by the orb. When being used, Tetsusaiga's blade becomes crimson red.
InuYasha learns Barrier shatter after he destroys the bat-demon Taigokumaru.
The Barrier shatter has been used the following times:
- During his fight with the Panther Devas 
- Piercing through Naraku's barrier immediately before hiding himself at Mount Hakurei.
- Tearing through a rat demon's barrier.
- Destroying the locks on the gate to the Netherworld, while battling the two underworld statues Gozu and Mezu.
- Trying to destroy Hakudōshi's barrier while riding Entei (unsuccessfully).
- InuYasha's last time performing Barrier shatter within the anime is against Naraku before he learns the Kongōsōha, though that is not the case with the manga.
- Attempting to tear through Midoriko's barrier which was keeping him away from Kohaku.
- Trying to save Kagome from Hitomiko
- InuYasha uses it at the beginning to break Naraku's barrier. 
- He uses it to enter Kaguya's fortress on the lake's surface.
- Though not exactly used, Tetsusaiga's blade glows red but for no apparent reason, perhaps because InuYasha thought Kaguya may be forming a barrier.
- To try and break through the barrier protecting the jeweled comb-box that held the power orbs of the Four War Gods.
Kongōsōha (金剛槍破, Diamond spear wave, Adamant barrage in English dub): the attack where the blade of the Tetsusaiga pulsates and slowly forms into a whole blade of fragmented diamonds. When the sword is whipped into an attack, many shards of spear-like diamonds shoot out with the ability to penetrate any barrier, which is particularly useful against those that the Barrier Shatter cannot break.
At his father's grave, InuYasha gained Kongōsōha indirectly from Hōsenki, a crystallized daiyōkai. Hosenki told InuYasha to cut him, but when InuYasha physically couldn't (which Hosenki probably knew), InuYasha decided that, instead of continuing to try, he would save his friends from Naraku instead. Thus, InuYasha obtained the power to combine his Kaze no Kizu with the kongōseki ("diamonds") to wreak havoc on the foe, or simply to swing Tetsusaiga and fire off a huge volley of large diamond shards.
While trying to get away from an ogre's belly Inuyasha used a jewel shard to power up his Adamant barrage into a more powered up form of the wind scar barrage or the Kaze no Kizu-soha called the Golden Gun.
In the manga, the yōkai Mōryōmaru was able to copy this attack. In InuYasha's case, it can be fired with or without an accompanying Kaze no Kizu. Mōryōmaru appears to be able to use it with the same or slightly less power than InuYasha, in any case he was able to mince Naraku to the same degree.
Youki absorption / Youketsu cuttingEdit
The acquisition of the Dragon-Scaled form gave Tetsusaiga the ability to theoretically absorb limitless amounts of youki, but because of Inuyasha's nature of as a han'you, he could not use this ability to its fullest extent without incurring potentially fatal penalties. This forced him to develop another technique which enabled him to "sense" a youkai's youketsu, then cut it with the Dragon-Scaled Tetsusaiga; by destroying this source of a youkai's youki, Inuyasha can effect a sort of instant-kill upon a youkai, or if its a gestalt entity like Moryomaru, systematic destruction of the creature by the death of its component parts (which it can't regenerate).
Meidou Zangetsuha is an ability that creates a path to Hell (or a Meidou) through which to send an opponent; its perfected form is that of a large black sphere that resembles a hole in space. One can create a Meidou where the cut is made, or it can be fired like a projectile (its common application). InuYasha's father stole the ability from a yōkai named Shishinki with the aid of Tetsusaiga. However, because of the danger associated with such an ability, Tenseiga was created out of Tetsusaiga to bear it. InuYasha's father intended for InuYasha's brother Sesshomaru (a full yōkai who can withstand the terrible jyaki of Hell) to master that ability when he inherited the Tenseiga, then later have the sword reabsorbed into Tetsusaiga (thereby granting InuYasha the perfected technique).
Inuyasha later acquired this ability after Tenseiga is broken over Tetsusaiga, causing the latter to transform into a black blade that shares a resemblance to the physical appearance of a Meidou. Inuyasha then uses the new Black Tetsusaiga to re-open the Meidou to create a path back to the normal world for him and Sesshomaru. 
Inuyasha plans to use the Meidou against Magatsuhi but Magatsuhi dodges it with his self-Dispersion to Inuyasha's friends so he can't use the Meidou because it will swallow his friends as well. Inuyasha also uses this attack multiple times against Naraku after he gains the complete Shikon no Tama. First against his outer body, second against Sesshomaru while Magatshi controls him and finally against Naraku but they are all unsuccessful
During Inuyasha and his allies' final battle against Naraku, the Meidou's form underwent a transformation to signify Inuyasha's true ownership of the ability, with the new form reflecting Inuyasha's fighting style and Tetsusaiga's inherent nature as a "sword that cuts". When Sesshomaru nurtured the technique it developed to reflect Tenseiga, a sword that does not cut and the nature of Sesshomaru; hence a perfect circle. Inuyasha's mastery of it reflects his sword, which is one that cuts, and his temperament. As such, the new attack consists of several blade-like Meidous being fired, cutting through anything they touch. 
Tetsusaiga's transformations and abilitiesEdit
- Rusty form
- Tetsusaiga's basic form when in InuYasha's human hands or those of another human. Despite its appearance, it can still be used as any other sword and repel most yōkai with its other forms.
- Transform; True form
- With InuYasha's power fused with the Tetsusaiga, the katana becomes a giant fang with fur flickering at the hilt. This can block and of course use any of his "weapon techniques" It is also known that the Tetsusaiga can keep InuYasha's yōkai form from emerging.
- Defeating a bat daiyōkai that could put up virtually indestructible barriers with a red orb, InuYasha broke the orb with his Tetsusaiga and absorbed the blood from the bat demon, allowing him to break small barriers. This mode can also use the Wind Scar.
- Diamond (Adamant)
- An ability granted by the powerful daiyōkai Hōsenki. Tetsusaiga's blade transforms into a crystalized state that when swung shoots out hundreds of massive, razor-sharp diamond (or Adamant, as called in the English anime) shards that can slice through anything. It can as well be used conjointly with the Wind Scar or the Backlash-Wave (as seen in the end of the Fourth movie).
- Dragon-scaled Tetsusaiga(龍鱗の鉄砕牙, Ryūrin no Tetsusaiga)
- Another form of the Tetsusaiga gained in the manga after the anime ended. Tetsusaiga would destroy the sword Datsuki, and gained its ability to absorb youki through its dragon scales. However, the subsequent confrontation with the yōkai Dokumizuchi would reveal that due to InuYasha's nature as a han'you, Tetsusaiga cannot absorb huge amounts of youki without causing a catastrophic reverse-flow of energy. InuYasha would temporarily remedy this problem by absorbing the senki of the yōkai Nikosen, which purified the youki that the Dragon-scaled Tetsusaiga absorbed. But an embarrassing encounter with Sesshomaru, Tōtōsai, and the yōkai Numawatari would cause InuYasha to learn that he didn't "understand" the nature of Tetsusaiga by simply absorbing youki with its Dragon-scale form. InuYasha would be directed by Tōtōsai towards the yōkai-sennin Yourei Taisei, who would train him how to sense a yōkai's youketsu (a floating whirlpool of youki that is the source of a youkai's youki), and how to cut it with the Dragon-scaled Tetsusaiga (rather than use it to absorb the youki). InuYasha was then able to understand the Tetsusaiga's nature as "a sword that cuts", and his training was completed with the acquisition of Yourai Taisei's exceptionally-powerful youki, when he cut through his youketsu with the Dragon-scaled Tetsusaiga. The yōkai-sennin would silently indicate that the Dragon-scaled Tetsusaiga has one final form that he would leave to InuYasha to discover on his own. This could have hinted at an ability of the dragon scaled Tetsusaiga that Inuyasha discovers later, Cutting his own Youketsu, this allows Tetsusaiga to absorb Inuyasha's youki, it is then increased and flows through Tetsusaiga back to Inuyasha, this technique allowed Inuyasha to "charge up" and make his own youketsu larger than Shessoumaru's perfect Meidou, thereby overcoming it, and absorbing it into Tetsusaiga.
- The most recent form acquired by Tetsusaiga in the manga, after Tenseiga is broken over it. Tetsusaiga's blade takes the appearance of a Meidou, and is now capable of using the Meidou Zangetsuha ability.
- Sheath of Tetsusaiga (Tetsusaiga no Saya)
- Can deflect or resist demonic energy attacks with the barrier used to contain Tetsusaiga's power. However it can only withstand a limited number of attacks. The sheath can also summon the Tetsusaiga to itself, as seen when Inuyasha was trapped inside the flask of a sage with only the sheath. It was made from the freely given wood of Bokusen'on, an ancient sapient tree, and inherits its magical abilities from it. In one episode this tree deity explains to Sesshomaru the meaning of the two swords and what his father, the Great Dog Demon Inu no Taisho intended. This would also suggest that Tenseiga's sheath boasts similar abilities. When InuYasha first uses the windscar, Tenseiga forms a barrier and protects Sesshomaru, which seems to confirm this.
- ↑ Tessaiga
- ↑ Volumes 48, chapters 477
- ↑ Episodes 76-77
- ↑ 4.0 4.1 4.2 InuYasha the Movie: The Castle Beyond the Looking Glass.
- ↑ InuYasha the Movie: Fire on the Mystic Island.
- ↑ Volumes 51, chapter 503-504
- ↑ Volume 55, chapters 546-547
- ↑ Volume 40, chapter 391
- ↑ Volumes 40-41, chapters 396-399
- ↑ Volume 42, chapter 412
- ↑ Volume 43, chapters 423-425
- ↑ Volumes 43-44, chapters 426-431
- ↑ Volumes 51, chapter 503