Osamu Kasai is a Japanese composer, sound designer, and audio producer who has been working on video game music for over 20 years. Osamu started his video game music career in the 1980's when he worked for Advance Communication Company. While working there, him and Masaaki Harada composed the music for many of their titles, mostly for the Famicom. Since Advance Communication ported the Ys games to the NES and SNES, him and Masaaki had to re-arrange the original tracks to the NES, which was a difficult task. Kasai and Harada later started working as audio directors for Konami and have been working there ever since. Besides audio, Kasai has also been credited for game design and programming.
Kasai no longer composes music, but he still plays it on the piano.
Osamu utilized a sound driver titled Sound Routine. Music was most likely written in either 6502 assembly machine code or Music Macro Language. Some note octave errors in Sansara Naga (FC) suggest the latter. However, Michiharu had said his music was written in assembly.
Also, Osamu may have had a hand in programming the sound driver, as he has been credited for programming.