Beaver Joe is an esper beaver that was imprisoned and forced to fight in the "Esper Underground Arena".
Beaver Joe has the appearance of a normal beaver.
While in the "Esper Underground Arena" Beaver Joe is shown to be particularly violent and ruthless, having no qualms about killing a pleading Yasai Kuuka or using the arena announcer as a human weapon to hit Rinka Urushiba.
Rockswim: Beaver Joe, by the Glowing Fish, has been given the ability to control and manipulate rocks. He mainly uses his powers to clad himself into a enormous lizard-like rock armor and to launch a barrage of rocks towards his target at great speed.