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 Tsukuyomi-s 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 Hijiri-s younger stepsister, Yuika. But what should be an easily resolvable event quickly gets out of hand when Kousuke realizes that he-s entered a new route that not even he knows about!