|“||When kira ran through my body... it felt like I touched Yoite's life... or his heart. It felt lonely. But for some reason... it felt gentle too...||”|
–Gau, Chapter 43
- Nabari no Ou: Major character
- Nabari no Ou (Anime): Major character
- Garden of Children's Hearts: Cameo; 4koma
- Scissors and Lemon: Cameo
- Nabari Drama CD Vol.1
- Nabari Drama CD Vol.2
Gau is a lean boy with fluffly black hair, and cat-like brown eyes. He is most often seen wearing different variants of his school uniform while still a student, even while on the job as a Wakachi. While working at HONEY, his uniform consists of an apron with "HONEY" and a large honeybee on the front, which he wears over a sweater vest and a short sleeved dress shirt with a tie. His other casual clothes seem to consist of more sweater vests, cardigans, and the occasional hooded jacket.
While working as a Wakachi, he can be seen wearing a ying yang bracelet on his right hand, a symbol of his division in the Grey Wolves.
In the latter volumes, he can be seen wearing matching outfits with Raikou: when Raimei finds the pair after they had defected from the Grey Wolves, Gau wears a butterfly pin over his heart, which Raikou can also be seen wearing in the same spot. In the epilogue, he and Raikou are wearing matching cardigans, Gau's in black and Raikou's in white.
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.
Three years ago, 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.
- In Japanese culture, the symbol of the butterfly is often associated with departed souls, as well as metamorphosis and transformation, among others. During the scene in which the pair are seen wearing these pins, they can be seen praying for the deceased members of the clan, and discussing their desire to rebuild the Shimizu clan, making it a fitting motif for the scene, and for the revival of the clan.
- He is a percussionist in his school band.