Magical Explorer, Vol. 4 (light novel)

After clearing forty layers of the Tsukuyomi Academy Dungeon solo in record time, Kousuke is finally invited to join Tsukuyomis influential Three Committees. As he continues to do everything he can to ensure he and his friends get a happy ending, Kousuke senses that something strange has happened to Iori Hijiris younger stepsister, Yuika. But what should be an easily resolvable event quickly gets out of hand when Kousuke realizes that hes entered a new route that not even he knows about!