S1E21 — Shizu-san's Students
That Time I Got Reincarnated as a Slime — Season 1, Episode 21.
Rimuru becomes the new teacher for Shizu's students. However, having been summoned into this world against their will and facing shortened lifespans as a result, the children's feelings are complicated, and they're reluctant to accept Rimuru. So Rimuru proposes a series of mock battles with each of them to ascertain their abilities and allow them to let off steam.
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