You're watching two completely different anime universes collide for no reason other than pure comedic chaos. Rimuru's overpowered slime team meets Yohane's scrappy idol squad, and the entire joke is that power levels don't matter when the writing just wants to watch them bounce off each other. It's fanfiction energy in the best way, made official, weirdly charming, and aware the whole time that this shouldn't work.

Two franchises meet in this two-episode comedy fantasy ONA, a collaboration that brings the cast of Tensei Shitara Slime Datta Ken together with the world of Genjitsu no Yohane: SUNSHINE in the MIRROR. Without warning, Rimuru and his Tensura Team find themselves squaring off against Yohane and her Maboroshi Yoha Team. Rimuru's group looks to have the upper hand by a wide margin, leaving open how the clash between the two sides will play out.