Tenseiga

The Tenseiga (天生牙) is a fantasy sword from the anime and manga series InuYasha.

History
The Tenseiga is wielded by Sesshomaru, who inherited the sword from his father upon his death. The swordsmith Tōtōsai created it along with the Tessaiga from the fangs of Sesshomaru's father, who was a daiyōkai (lit. great yōkai) dog demon famous throughout the lands. 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.

Sesshomaru despises the Tenseiga for its lack of destructive power and early in the story, would attempt to acquire InuYasha's Tessaiga 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 him 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 kills him while under the corruption of the Tōkijin.

Abilities
The Tenseiga is a sword which can bring the dead back to life by allowing a powerful user to see the pall bearer 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, allowing the soul to return to the dead body. As the dead body revives, their mortal wounds are healed. It is important to note that Tenseiga cannot really heal the living; it resurrects the dead. 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. It is later reforged into a weapon capable of killing an opponent in a single blow along with its aforementioned powers of revival.

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 resurrect the dead, Tenseiga has also the ability to protect its user 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.

Inheritance
It is possible that Inu no Taishou intended that Sesshomaru and InuYasha inherit Tenseiga and Tessaiga 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 Tessaiga to protect himself and his loved ones and defend himself against Sesshomaru. Additionally Tessaiga 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 Tessaiga'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 Tessaiga can cut down 100 beings with one strike.

In Ch.495 it is further revealed that Inu no Taishou meant for InuYasha's Tessaiga to eventually reabsorb Tenseiga later on, apparently leaving Sesshomaru with nothing. The reason for this, in the words of Tōtōsai, "Throw it all away Sesshomaru... your attachment to your sword, your hatred for InuYasha... when that happens, Sesshomaru, you will have surpassed your father."

New Abilities
Tōtōsai later reforges the Tenseiga after Tōkijin is broken. The Tenseiga detected a change in Sesshomaru's heart when he felt feelings of fury and sadness for Kagura. The fact that Sesshomaru had finally 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. 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 Tessaiga. However, the ability was deemed too dangerous to be retained due to its nature, and Tenseiga was created out of Tessaiga 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 Tessaiga, allowing him to create a perfectly-circular Meidou that is bigger and and more powerful than Shishinki's version. He has since then been able to create a perfect Meidou at will, even outside Tessaiga'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 Tessaiga 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 currently 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 Tessaiga'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 Tessaiga 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 Tessaiga, causing the latter to transform into it's Dragon-Scaled form. Tessaiga 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 Tessaiga, causing the mirror shards to be swept away and the former sword itself to be broken. Tessaiga 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 Tessaiga 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...

Swords of an Honorable Ruler
Tenseiga plays a major role in the third movie, along with InuYasha's sword Tessaiga 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 (even though Myōga berates him for sealing the sword for only 200 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 strangely performed by Tenseiga instead of Tōkijin).

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, but is never seen in the manga--though 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.