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.
Kotobuki began playing keyboards and guitar for Morio Agata's tours in the early 1980s. Following Agata's tour, he and Agata formed a band named the Yukiyama Brothers.