Mizuchi

was a water dragon yōkai who poisoned Inuyasha using its toxic breath. In the end, however, Inuyasha killed it using his Tessaiga.

History
Mizuchi originally lived at the bottom of a lake and ate a a piece of flesh of Mōryōmaru, which he deliberately dropped into the water to be consumed. Inuyasha and his friends became aware of Mizuchi by the residents of a village near the lake. According to them, the Mizuchi had recently become particularly bloodthirsty. A group of samurai who went to destroy Mizuchi were skeletonized by his strong poison breath.

Inuyasha lured the water dragon with his Kaze no Kizu from the lake. He asked him if he knew Mōryōmaru, as his smell resonated from his body. The water dragon denied this and immediately attacked Inuyasha with his poison breath. Inuyasha absorbed the poison with the newly acquired Dragon-scaled Tessaiga, but Tessaiga heated by the absorbed yoki. Thanks to trick by Byakuya, who observed the fight on behalf of Naraku, the water dragon multiplied and attacked again. Inuyasha then used his Kongōsōha as a recourse. Mizuchi was injured by the diamond spears and fled to the lake when he promised his revenge to Inuyasha, while Miroku absorbed the remaining poison with his kazaana.

The following night, when Miroku recovered from the poison, Inuyasha is visited by Byakuya, who informed him that Mizuchi has been strengthened by Mōryōmaru's flesh, which is why he would not die when Inuyasha cut him up, and he could only defeat him by depriving him of his entire yōki with the Dragon-scaled Tessaiga. In the ensuing fight, Inuyasha absorbed so much poison from Mizuchi with Tessaiga that its blade turned black and got even hotter than before. When Mizuchi attacked again, Inuyasha simply sliced Tessaiga through the poison and halved the water dragon in one fell swoop.

Since Inuyasha has absorbed Mizuchi's yōki, he could no longer regenerate. Inuyasha, however, experienced the dangerous energy recoil of the Dragon-scaled Tessaiga due to the huge amount of yōki he has absorbed with it. He is badly injured and lies on the ground. Byakuya suggested that he would be willing to offer himself as a second opponent for Inuyasha, but Kagome, Miroku and Sango stand in front of him, whereupon Byakuya fled and says that his job is only to watch for the time being.

Afterwords
In a conversation with Tōtōsai, Inuyasha later learned that the energy recoil would have killed him if he had not pulled back on absorbing Mizuchi's yōki.

Physical description
Mizuchi had the long body of a snake with a human-like head with two small horns, pointed fangs, and long black hair.

Strengths & Abilities

 * Poison Breath: Mizuchi spewed huge, circular poison clouds that were strong enough to wilt trees and skeletonize humans. Mizuchi himself said that Inuyasha could absorb as much poison as he wants, since it would never run out.
 * Regeneration: After consuming Mōryōmaru's flesh, Mizuchi gained the ability to regeneration his body. This made him invincible to all physical attacks, and could only be killed after his yōki is absorbed.

Media appearances
Mizuchi