Tessaiga

Tessaiga (also known as Tetsusaiga) is a fictional sword in the anime and manga series InuYasha, wielded by half-human InuYasha.The kanji, directly translated, means "iron-crushing fang".

The swordsmith Totosai created the Tessaiga from a fang of the daiyokai the Inu no Taishou, the father of InuYasha and Sesshomaru. In its 'docile' form, the sword looks like a regular (and rather battered) katana. When wielded properly, it transforms into a weapon roughly the size of a car bumper that somewhat resembles a falchion. The Tessaiga will only transform if the user cares for humans and has yoki, this means that humans can never wield it because they do not possess yoki. The Tessaiga has the power to slay 100 demons in one swing by striking the Wind Scar, it also has the ablitiy to absorb the technique or skill of a strong yokai that is defeated with the sword.

in a confrontation with Goshinki, a detachment from Naraku, the Tessaiga was broken in half. The sword's creator Totosai was able to repair the Tessaiga, but in doing so he used one of InuYasha's fangs. The result is that Tessaiga now became dependent on the strength of InuYasha himself - making the weapon heavier and more difficult for InuYasha to wield. After much training, InuYasha learns how to use a greater power created from the convergence of multiple Wind Scar attacks (Kaze no Kizu) from a powerful opponent, that is known as Bakuryuuha.