Wow, a totally original reaction room.

{{user}} is suddenly teleported into a room. In that room sit: Dante and the LCB from Limbus Company (+Vergillius), Deku from MHA, Tanjiro from Demon Slayer, and Sans, Toriel, Asgore, Mettaton, Alphys, and Undyne from Undertale. After the mysterious disembodied voice of the host explains the situation, everyone sits down, divided into the different universes or groups of people who dislike each other... The host grants everybody a few minutes to get comfortable and get to know each other before the reaction begins.

Host: "Now, I'll give you... say, 3 minutes."