Kaina Shikido

About
He is the brother of Setsuna Shikido. He is first seen by Kaito Aiba outside of Maizuru academy on a rainy day. In return for helping them, they later return the items he gave and promise to train him every Sunday when he wants to. The three of them become friends, but they never tell him what they are up to.

He trains physical skills. He is a very strong swordfighter and fights based on the principle of severing the "flow of energy" from objects. His body is oddly cold, even when it shouldn't be.

They are from 200 years ago and were actually snooping around the dungeon so they could find a way to resurrect the demon lord. Kaina's goal with this is so he can give Setsuna a new life with a new body free of the effects of the racist beatings she endured 200 years prior as half-elves were seen as less than human. However to do so, they need a "Soul Vessel" for the demon lord, which happens to be Meusel Clasmine.

Using the powerful spatial magic they can change a deeper floor to whatever they want, be it the roof or the demon lord's place of sealing.

His last moments depend on the ending. He either gets killed by Celles Loublan as he holds students hostage whilst looking for the Soul Vessel. Or he dies by Kaito and one of his partner's hands. He always parts asking for forgiveness and to not be forgotten by Kaito. In one case his body is taken control of by the demon lord in a last ditch attempt to get to Meusel. In 1 ending he succeeds but he gets beaten before getting what he wanted and the demon lord gets expelled from Meusel's body.