Poppen-sensei to Kaerazu no Numa

Overview

While eating lunch by the swamp located on Udo University's campus, Professor Poppen's wristwatch suddenly stops. A strange and life threatening adventure begins as the professor transforms into various wild life of the swamp. Will he ever be able to return? Based on the children's book series by Yoshihiko Funazaki called Poppen-sensei, which follows an assistant biology professor at Udo University who gets wrapped up in his fantasies of nature.

Source: AniList