Utsurun desu.

This manga is deemed to be one of the works that initiated the "irrational" or "unreasonable" gag comic genre where the reason of its funniness cannot be explained by logic and traditional sense of humor, which made this title very popular among teens and early twenties at that time. One of the most popular characters that appeared in Uturun desu. was "the otter," Kawauso-kun.

(Source: Wikipedia)