Kuroo and Kenma are childhood friends and every since childhood Kuroo was interested in volleyball and always made Kenma play with him, Kenma didn't really want to play volleyball but played for Kuroo and once they were in high school they were in the school Nekoma and the two joined the volleyball club and about a year the two had met Yaku and Lev in the volleyball club and eventually the four of them started dating each other and six year time skip the four was now adult and living together.