His debut as a video game composer came with Crystal Software's "Mugen No Shinzo III" in 1989 with Chihiro Fujioka. After sending his demo tapes and résumé to every software house and game company listed in the PC-specialized magazines, he got one response from Micro Cabin. He went on to compose music for three "Xak" games along with Tadahiro Nitta: ', "Fray in Magical Adventure", and '. During this time, he was working as a freelance composer. In 1991, after Fujioka had been hired as a director for Square, Sasai was invited to join the company as they needed composers to assist Nobuo Uematsu and Kenji Ito. His first assignment was to create the soundtrack to the Game Boy title "Final Fantasy Legend III". Sasai composed the majority of the score, with director Fujioka handling four pieces.