Hagiwara Ataro was just playing video games in his apartment when a girl came crashing through the wall. His next door neighbor should have the same room as he does, but what he sees on the other side of the wall is a whole labyrinth of a dungeon. The girl’s name is Kris, a cute, shy human girl who seems to be hunted by succubi and she explains to him that misfired magic in her world sometimes causes dimensional rifts into Ataro’s world. But there is another person inside Kris. She becomes Seres when she takes a potion created from her ring which changes her appearance and, more importantly, makes her incredibly strong. Ataro, now trapped in a different dimension, has to follow the Kris/Seres pair if he wants to find his way back home.