
Quick answer — Ryoutarou Okiayu worked on Tennis no Ouji-sama: Zenkoku Taikai-hen (Theme Song Performance), Tennis no Ouji-sama: Zenkoku Taikai-hen Semifinal (Theme Song Performance), Onegai My Melody (Theme Song Performance).
Ryoutarou Okiayu worked on Tennis no Ouji-sama: Zenkoku Taikai-hen (Theme Song Performance), Tennis no Ouji-sama: Zenkoku Taikai-hen Semifinal (Theme Song Performance), Onegai My Melody (Theme Song Performance).