In the KonoSuba world, Kazuma Satou's party comes across a big red button. Meanwhile in the Overlord world inside the Great Tomb of Nazarick, Ainz Ooal Gown receives reports from Floor Guardian Demiurge of strange red buttons randomly appearing throughout Nazarick. Megumin intentionally pushes the button and soon Ainz follows by setting theirs off as a result of accidentally sitting on one that suddenly appeared on his throne. Both series' casts are sent to another world featuring a school...