Isekai Quartet

In the settings of Overlord, Saga of Tanya the Evil, and KONOSUBA, a mysterious button device appears. Someone accidentally or intentionally pushes it, and the core casts of those settings find themselves transported to a new world which looks suspiciously like a modern Japanese high school. They all find themselves compelled to participate in a class led by a character from Re:Zero at a school led by officers from Saga of Tanya the Evil, and soon they are joined by core members of the Re:Zero cast as well. Typical school antics ensue with a far-from-typical student roster.

Synopsis from Anime News Network