Nagamushi

Nagamushi (大蛇, Serpent) is a spiritual entity sealed inside Neiru Hyūga. It is said that Nagamushi was born from the rebirth and change of the shinobi world. Every few years or so, Nagamushi would select someone worthy enough of becoming it's vessel. Upon being sealed into a worthy human, it thrives off of the transformation of a human based off of the vessel's desire.

Neiru Hyūga wanted to see his friend again. Neiru's heart would change upon being reunited with him, thus feeding Nagamushi.