The Tenseiga is wielded by Sesshomaru, who inherited the sword from his father upon his death. The swordsmith Tōtōsai created it along with the Tetsusaiga from the fangs of Sesshomaru's father, who was a daiyōkai (lit. great yōkai) dog demon famous throughout the lands. Totosai jested that its original name was going to be the coffin cheater but called it Tenseiga instead. Tōtōsai claims that only someone who has the heart to cherish others would be able to use it, but confesses that he has actually little clue to the sword's mysterious powers. Sesshomaru, surprisingly, is able to use Tenseiga's abilities. According to Tōtōsai, Tenseiga has chosen Sesshomaru as its master, regardless of whether he had a kind and caring heart and declares that whether it is to prosper or wane is up to Sesshomaru's heart.
Sesshomaru despises the Tenseiga for its lack of destructive power and early in the story would attempt to acquire InuYasha's Tetsusaiga using whatever means he deemed appropriate. Tenseiga has been used sparingly, mostly only when Sesshomaru feels like using its power for his own gains such as reviving the head of the yōkai Goshinki so that his fangs can be used to create the sword Tōkijin; or when the sword compels Sesshomaru to use it for a good cause. One such example was the sword pulsing to tell Sesshomaru to revive Kanta's father, and in so doing, Sesshomaru learns the demon graveyard his father resides in figures into Naraku's plans.
Sesshomaru's human companion, a human girl named Rin, is brought back to life with the Tenseiga after she was killed by the demon wolves of Koga; Jaken, Sesshomaru's assistant, is revived by Tenseiga as well after Kaijinbō cuts him in two halves while under the corruption of the Tōkijin.
The Tenseiga is a sword which can restore life by allowing its master to see the pallbearer demons that take away the souls of the dead. As Tenseiga has the power to connect to the underworld, these demons can be cut and destroyed by it, save the soul from being taken. As the dead body revives, their mortal wounds are healed. However, no being can be revived by Tenseiga more than once. This is so the Tenseiga will never be able to bring about eternal life. The body of the being that is to be revived also needs to have all its parts in order for complete resurrection. An example of this was Goshinki's head. While resurrected by Tenseiga, only his head was restored to life since the rest of his body was annihilated by Inuyasha. It is important to note that Tenseiga can only restore life if the pallbearers are present. The literal translation of the kanji is "heavenly life fang" or "fang born out of heaven", but these are not necessarily accurate representations of the name's actual meaning.
Tenseiga allows its user to see and slay the beings from the underworld, as well as bringing up to 100 beings back to life in one swing. Since Tenseiga can harm the beings of the netherworld, the guardians at the gate that separates the Living World and the Dead, Gozu and Mezu, will not attack anyone who wields the Tenseiga for fear of their own safety, thus allowing them to pass the gate unobstructed.
Other than the power to restore life, Tenseiga has also the ability to protect its master by erecting a barrier in extreme cases or life-threatening situations. When InuYasha unleashed the Wind Scar properly for the first time on Sesshomaru, Tenseiga, sensing that the blow was fatal, gave off a blue light surrounding him and teleported him to safety. This seems to be a built-in defense mechanism. Tenseiga has also protected Sesshomaru in several other dangerous situations.
It is believed that Inu no Taishou intended that Sesshomaru and InuYasha inherit Tenseiga and Tetsusaiga respectively so that they could not kill each other. Likely knowing that Sesshomaru despised InuYasha for being a hanyou and that Inuyasha would have a dangerous life, Inu no Taisho gifted InuYasha with the powerful, destructive Tetsusaiga to protect himself and his loved ones and defend himself against Sesshomaru. Additionally Tetsusaiga seals InuYasha's full demon blood.
Sesshomaru was given the Tenseiga, such that Tenseiga could never be used to kill InuYasha and can protect him from Tetsusaiga's attacks. This could be planned by Inu no Taishou to instill brotherly kinship or at least respect among the two brothers. Both swords are compared by Tōtōsai as two sides of a coin. Neither is superior or inferior to the other. Each cancels out the other as Tenseiga can save 100 lives with one strike while Tetsusaiga can cut down 100 beings with one strike.
Tōtōsai later reforges the Tenseiga after Tōkijin is broken. The Tenseiga detected a change in Sesshomaru's heart when he felt anger as Mōryōmaru was mocking Kagura's death. The fact that Sesshomaru had felt compassion for others prompted the Tenseiga to call out for Tōtōsai to reforge it.
The sword gains the Meidou Zangetsuha, which allows it to send enemies directly to the land of the dead as well as its previous resurrection power. Tenseiga allows its user to cut open the path or boundary that separates the worlds of the living and the dead. A dark arc is formed in which it "cuts" the enemy in a sense and sends it to the after life. Sesshomaru performed this attack successfully on his first try which surprised Tōtōsai. In the beginning, the fissure was only crescent moon shaped. As Sesshomaru perfects the technique the arc will become closer to a circle which will be able to send the entire body of the enemy to the next world or hell. Thus, Sesshomaru finally accepts its potential as a weapon.
Sesshomaru has used this technique numerous times and seeks to improve himself by entering a mountain and training by killing demons living there. Not that it was relatively weak to begin with, since a single hit to an opposing target is almost always enough to ensure a sure-fire one-hit kill even to the powerful Numatari. Later, he kills the Numawatari (demonic lake), which InuYasha and his companions could not defeat, with a single blow. He is closer to mastering it in chapter 470, when he purified many dead bodies, widening the opening.
In Ch.470, it was revealed by Sesshomaru's mother that a person cannot be revived by Tenseiga more than once. He realizes this when Rin, already dead, is not responding to Tenseiga and vice versa. However, at the end of Ch.471, Sesshomaru's mother apparently revives Rin using the Meidouseki, after leaving the Land of the dead.
Sesshomaru would encounter the mysterious Shishinki, a yōkai with half a face that claimed to have fought Inu no Taishou in the past. It would be revealed that the ability Meidou Zangetsuha was originally his own, and that Inu no Taishou stole it from him with Tetsusaiga. However, the ability was deemed too dangerous to be retained due to its nature, and Tenseiga was created out of Tetsusaiga to bear it. Inu no Taishou intended for Sesshomaru to master the ability, as only a full yōkai like himself could bear the terrible jyaki that is associated with Hell itself. Although the "incomplete" nature of Tenseiga is seemingly preventing Sesshomaru from mastering the ability on his own, Sesshomaru was finally able to master it when Tenseiga resonates with the nearby Tetsusaiga, allowing him to create a perfectly-circular Meidou that is bigger and more powerful than Shishinki's version. He has since then been able to create a perfect Meidou at will, even outside Tetsusaiga's presence.
However, Sesshomaru is haunted by the revelations stemming from the confrontation with Shishinki and meets with Tōtōsai, at which point he deduces what he believes to be his father's intent for Tenseiga: that it be re-absorbed into Tetsusaiga after Meidou Zangetsuha has been perfected by Sesshomaru, and consequently, granting InuYasha the perfected ability. While Tōtōsai doesn't deny this, he further adds that were Sesshomaru to go beyond his attachment to Tenseiga and resentment towards InuYasha, he would finally surpass his father.
This sets the stage for a winner-takes-all battle for both swords between the two brothers. A sinister element is further added to the conflict in the form of Naraku and Byakuya, who previously provided Sesshomaru with a fragment of Kanna's mirror monster, which allowed Tenseiga to steal Tetsusaiga's abilities, while also morphing into a replica of the latter sword that can use said abilities. InuYasha counters this disavantage by once again transforming into his full yōkai form and empowering the now-powerless Tetsusaiga with his own youryoku, which also has the added effect of reclaiming the sword's stolen abilities by crossing swords with Tenseiga. Sesshomaru then fires off a Meidou, which begins to suck InuYasha into Hell; seemingly victorious, the former discards Tenseiga into the Meidou, having lost any desire for it. However, this causes the sword to resonate with Tetsusaiga, causing the latter to transform into it's Dragon-Scaled form. Tetsusaiga then instructs InuYasha to cut his own youketsu, which instead of killing him, causes a massive surge of youki powerful enough to erode the Meidou; Sesshomaru surmises that this is perhaps the proof of InuYasha's worth as the successor to both swords. After Naraku seizes control of Tenseiga (through the mirror shards) and injures InuYasha with shouki-infused diamond spears, Sesshomaru enters the Meidou and retakes Tenseiga, making Naraku believe that the yōkai is out to finish off InuYasha himself. However, Sesshomaru instead swings Tenseiga at Tetsusaiga, causing the mirror shards to be swept away and the former sword itself to be broken. Tetsusaiga then transforms into a black blade that resembles a Meidou, apparently with the power of Meidou Zangetsuha. The brothers are then guided out of the Meidou by the reformed Tenseiga, which had fallen out of the Meidou and was giving off a bright light that served as a "beacon" for the Black Tetsusaiga out of the darkness of the Meidou. Sesshomaru departs without Tenseiga, but Rin takes it herself before she and the rest of her party followed the youkai. Totosai surmises that although Sesshomaru doesn't realize it himself, he's one step away from possessing something that's not his father's memento, but his very own weapon...
This Weapon is later revealed, Bakusaiga, when Sesshomaru regenerates his lost arm. The Sword appears in his hand when it is fully regenerated, and appears to be completely opposite of Tenseiga, instead of saving the soul of a person, it corrodes the flesh, and removes any regenerative properties.
Swords of an Honorable RulerEdit
Tenseiga plays a major role in the third movie, along with InuYasha's sword Tetsusaiga and their father's sword So'unga. When Saya, the spirit of the sheath, is no longer able to seal the demonic So'unga after 700 years , the So'unga is freed and goes on a rampage to destroy all of humanity.
InuYasha and Sesshomaru are forced to reluctantly work together since So'unga is only weakened by the two fangs themselves. They eventually defeat their father's sword by combining InuYasha's Bakuryūha and Sesshomaru's Soryūha (which is more likely to be the attack that saves 100 people in one stroke, but looks like the Soryuha because if it were the actual Soryuha Sesshomaru would not have needed to have Tokijin forged).
It was also observed in the third movie that Tenseiga has the ability to cut and damage the undead. Tenseiga's life giving powers deal divine damage to the undead, causing far more damage than conventional attacks. This happened another time in the anime to defeat the lord of the Panther devas. In the manga, when Sesshomaru confronts the guardians of the gate to the land of the dead, they observe that Tenseiga can wound those not of this world--including themselves. And in recent chapters, Sesshomaru uses the Tenseiga to cut the demon lord of Meikai (Hell) and Magatsuhi.