 If you liked
Tate no Yuusha no Nariagari
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 ...then you might like
Souen no Historia: Shintaku Shoujo no Biblion
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Both novels feature the familiar transported/reincarnated to a fantasy/game-like world from Japan theme.
In TnY, the main character is summoned into a different world but in Souen no Historia, the main character dies after saving a girl and is reincarnated into a different world. Both main characters become extremely OP, Naofumi from TnY is a 'hero' while Souji from SnH is an overpowered butler (think Hayate no Gotoku).
Both series feature harems and are enjoyable to read.