Three years ago, 17-year-old Gau was saved by Raikō and is thus extremely devoted to him. Infatuated and deeply grateful to him, he assists Raikō with his responsibilities to the Grey Wolves in the Wakachi, usually compiling reports and taking samples from their targets.
He believes Wakachi exists to protect the front world from the evils of Nabari. He is an idealist, who believes that the Shinra Banshou can be used to save the world. He knows Raikō's true motives behind the massacre of the Shimizu clan and is the one who reveals the truth to Raimei, offering his own life as proof that he was telling the truth.
When the siblings confront and fight against one another, Gau attempts to block Raikō's finishing blow to Raimei and receives the clear shot, slipping to comatose. Raikō refuses to sacrifice humans necessary to use Kōga Village's kinjutsushō to wake him up, and is in great distress as he blames himself for Gau's condition. Later on, it is Yoite who wakes Gau up with his kira technique. Gau feels deeply indebted to Yoite and chooses to support him and even goes against the Grey Wolves to aid Yoite. Unfortunately, Yoite goes beserk after Killing Hattori and that may cause the Iga Village and the Iga Clan to be destroyed by the hands of the Shinra Banshou.
Gau is easily incited and receives the nickname "Tenpa-kun" (テンパ君), from the slang tenparu (テンパる, lit. about to blow a fuse). He and Yukimi often quarrel nonstop over his dirty apartment room whenever him and Raikou comes over, to which Raikou quickly ends. Nonetheless, Gau has a strong sense of his duty, though easily swayed. He can be emotional over deeply felt situations, and is seen when he cried during Raikou's confession of his past. He admits to never having any associations to the Nabari world previously, and can't handle a sword fight properly.
- Gau admires Raikou. He's attracted to him and comes to the point of fantasizing about him.