Tensei shitara Slime Datta Ken OVA - episode 3 - 26 Mar, 2020

Rimuru, who is teaching Shizu's students as a substitute at the Kingdom of Ingrassia's Freedom Academy, takes part in an orientation in actual field combat in the school's annual outdoor training event. Transfixed by the prize he gets if he wins, he accepts a challenge from the teacher Jeff. However, an enemy appears before the students... (Source: Wikipedia)