I'm Standing on a Million Lives.

Ninth grader Yotsuya Yuusuke is practical, friendless, and not active in any clubs. Then one day, he and two female classmates are suddenly sent to another world where they must work together to battle for their lives. Yotsuya is a lone wolf and has always lived his life according to his wants, but how will that work out now that he’s supposed to be a hero?!