This is book number 2 in the Magical Explorer (light novel) series.
New school, new dungeons, new...maid?
At long last, Kousuke enters Tsukuyomi Magic Academy, the main setting of the erotic dating sim into which he’s been reincarnated. But between training every spare moment and using his knowledge of Magical Explorer to win the hearts of all the heroines he can, our hero’s student life turns out to be anything but easygoing. And that’s all before he activates a (literal) angel of a maid in the depths of a hidden dungeon!