 If you liked
High School DxD
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 ...then you might like
Kaifuku Jutsushi no Yarinaoshi
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Starts off with the main character being a normal individual but after the first episode he's involved into dangerous fights against monsters and villains. The protagonist becomes crazy powerful and he's surrounded by hot chicks that are ready to help him in their adventures. Redo of Healer has of course a more violent/edgier tone and it's way more borderline Hentai then DxD, but the concept for these two is extremely similar in my eyes