
Quick answer — Kenji Ootsuki worked on Hellsing Ultimate (Insert Song Performance), Zan Sayonara Zetsubou Sensei Bangaichi (Theme Song Performance), Sayonara Zetsubou Sensei: Nyankin no Kirisuto (Theme Song Performance) and 1 more anime.
Kenji Ootsuki worked on Hellsing Ultimate (Insert Song Performance), Zan Sayonara Zetsubou Sensei Bangaichi (Theme Song Performance), Sayonara Zetsubou Sensei: Nyankin no Kirisuto (Theme Song Performance), Prison School: Mad Wax (Theme Song Lyrics).