Kirishima, Ayato

Ayato Kirishima is Touka Kirishima's younger brother, and goes by the alias Black Rabbit. He grew up with his sister in the 20th ward but at some point in time, he left the district. According to Kazuichi Banjou, Ayato subsequently began to wander all the wards of Tokyo, bringing sheer wreckage and chaos upon them, until his unique powers and abilities caught Tatara's eye. Ayato was therefore pulled into joining Aogiri Tree, where he is currently an Executive.

Ayato is an arrogant, brash teenager, with a similar hot-blooded attitude resembling his sister's, while he normally displays either a scowl or menacing smirk on his face. Other than his physicalities, he shares many similarities with Touka, such as his tendency to use language that is often uncouth or inappropriate. He has a habit for kicking people over the simplest mistakes; such as when Kaneki failed to address him with the desired honorific, or when Banjou didn't return his missed calls. However, he seems to be more harsh compared to his sister, but admits himself to be surprisingly "softer" than his Aogiri superiors. He is a firm believer in the notion that 'the weak perish and the strong survive,' which was triggered by the death of his mother and father. Ayato bears deep grudges against his father, Arata, for abandoning him and Touka when they were young. Ayato has even stated that the whole reason for hating Kaneki was his resemblance to Arata. It was also pointed out by Kaneki that Ayato cares deeply for Touka subconsciously, as shown when he beat her down first rather than allowing her to suffer a slow, torturous death from Yamori. Later on, he also took her alias, "Rabbit" so that the CCG would hunt him instead of Touka. Ayato also seems to have a soft spot for rabbits.

Tokyo Ghoul:re:

Three years later, there is a reduction in most of the mannerisms and habits which Ayato once portrayed when he was younger; as he became far less ill-tempered, obnoxious and arrogant, and even developed a rational, approachable way of speaking. However, he still retained a few of his old traits, such as relentlessly slaughtering Ghoul Investigators and engaging in violent brawls.

(Source: Tokyo Ghoul Wikia)