Tensei Colosseum: Saijaku Skill de Saikyou no Onna-tachi wo Kouryaku shite Dorei Harem Tsukurimasu is a Manga in english language, Action series, english chapters have been translated and you can read them here. You are reading chapters on www.reincarnationcoliseum.com fastest updating comic site. The Summary is

High schooler Kouji Mikagami is painfully average in every way—except when he’s playing video games! So getting summoned to a magical world and granted the ability to copy his opponents’ skills should be his way to the top. But before he gets the chance, he’s thrown into the coliseum as a combat slave…for his trash-tier skill! In the midst of his despair, he realizes only one path remains open to him—beat down the strongest girls with the weakest skill and make a name for himself!