Rising Against the Odds: The Fujimoto Twins' Journey

Story is about a group of 4 friends from classic school who are struggling to survive in a world invaded by monsters and trying to rescue their friends. In the story, one of the members of the friend group chases after a monster that escaped through a crack in order to kill it, but ends up finding himself in the world of monsters. While the other friends wait for the crack to open again, they also wonder if they can open the crack themselves and try to do so. In the end, the humans enter the crack and start searching for the member of the group who is lost.