Isekai Quartet

is a Japanese anime series that serves as a chibi-style crossover between Kadokawa's isekai-genre light novels.

Plot
One day, a magic button suddenly appears. The protagonists in KonoSuba, Overlord, Re:Zero − Starting Life in Another World, and The Saga of Tanya the Evil all press the button and move to a parallel world — another brand new isekai — at where a new story featuring high school life begins.