Ayato Kirishima is Touka Kirishima's younger brother and Renji Yomo's nephew. He grew up with his sister in the 20th ward but at some point in time, he left the ward. 

Ayato 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 served as an executive before its downfall.

Later, he joined the new organisation Goat under the One-Eyed King.