I Want to Connect, so I'm Not Giving Up - S1.E6

The group rescue Haruka after he is kidnapped by Reo, and are transformed back into human form. Keppi explains that Reo and Mabu are agents of the Otter Empire, who have been at war with the Kappa Kingdom for generations over the energy of the shirikodama; with the Kappa Kingdom now defeated, the Otter Empire has begun to extract the shirikodama of humans. In a post-credits flashback set during the Otter-Kappa war, Mabu sacrifices himself to protect Reo in battle.