Extra: The Tragedy of M?

The first OVA of the anime adaptation of That Time I Got Reincarnated as a Slime.

Synopsis
One day, Shuna and Shion are fighting over Rimuru's squishy slime body as usual. Rimuru figures that giving them each a body double of himself would solve the conflict, but when he imagines some of his other friends asking him to do the same for them, he quickly drops that plan. Then he comes up with the idea to make a cushion in the shape of his slime form. He travels around Tempest to see if his friends know of any good materials he can use, and he learns that a special type of sand found along a lakeshore in the forest is exactly what he's looking for. So he sets out to collect some sand... but a monster is waiting for him by the lake! What's more, Milim hears about his plan for a picnic and comes racing down from the sky! The fun, relaxed story features the all-star cast of Jura Tempest Federation citizens enjoying a picnic by a lake, with never-before-seen scenes brought to you by the same cast and staff as the TV series!

Trivia

 * This OVA is bundled with the special edition of Manga Volume 12.