In the early 1980s, Kotobuki joined Morio Agata's tour as a keyboard player and guitarist. After Agata's tour, Kotobuki and Agata formed a band which they called the Yukiyama Brothers.
During the 1980s, Kotobuki began playing keyboards and guitar for Morio Agata's tours. Following Agata's tour, Kotobuki and Agata collaborated to form a band named the Yukiyama Brothers.