Quick answer — Koutarou Nishiyama voices Ryuuichi Kashima in School Babysitters, Kentarou Momose in My New Boss is Goofy, Hikaru Satou in MAJOR 2nd and 34 more characters.
Koutarou Nishiyama voices Ryuuichi Kashima (School Babysitters), Kentarou Momose (My New Boss is Goofy), Hikaru Satou (MAJOR 2nd), Yoshiharu Hisomu (Kiznaiver), Tsuzuru Minagi (A3! Season Spring & Summer), Jin Kougasaki (TOUGEN ANKI), Atsushi Kinugawa (Cute High Earth Defense Club LOVE!), Kazuhito Narita (HAIKYU!! 3rd Season) and 29 more.
Ryuuichi Kashima is voiced in Japanese by Koutarou Nishiyama.