Challenge from Underwater (E41)

The Ultra Guard suspects Kappa, a mythical creature, is responsible for a number of disappearances. Although the case has been taken on by a local club, when one of their partners gets kidnapped, Dan searches alone hurriedly. That's when he finds the missing hunter's dead body. While the UG and club are examining the body, they catch a glimpse of Kappa. They chase it into a lake, and it fades. (Prime Video)