That Time I Got Reincarnated as a Slime 1x20 Yuuki Kagurazaka - Trakt

The threat of Charybdis has gone. That night, Rimuru has a dream in which he sees Shizu teaching children at her school in the Kingdom of Ingrassia—a dream showing Shizu's lingering regret. To see her wishes through, Rimuru leaves the Jura Tempest Federation and heads for the capital of the Kingdom of Ingrassia. His first goal is to meet with the Grandmaster of the Guild, Yuuki Kagurazaka, who happens to be a Summon and a former student of Shizu's.

I was watching episode 20 of Tensei Shitara Suraimu Datta Ken and saw this reference : r/anime

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