Gepyo is a large green and brown striped frog creature. He originally lived in the water in the Taisai River, which was turned dirty by the Kingdom. He only says "Gepyo" or some variant of that phrase.
When attempting to fix the dirty water Dorian finds him in the dirty water of the Taisai River. Gepyo then lunges at Dorian and he doesn't like it, and then claims that Gepyo is one of the Kingdom's bad guys and wants to stop him.
Sewage Toad Gepyo is a boss that Dorian defeats at one point. He was corrupted by the dirty water and Dorian attacks him believing him to be one of the Kingdom's monsters. When Dorian attacks Gepyo, Gepyo spits out small brown tadpole creatures to attack Dorian and his Wood Spirits. He can also swallow Wood Spirits. After Dorian defeats Gepyo he gains a Mana Crystal. He then sets off to stop the Machine causing the dirty water, then uses the Purify magic spell to clean the water.
Gepyo changes appearance and starts talking normally to Dorian, and he says that he is Gepyo and that he is the keeper of the lake. He explains that he used to live peacefully in this lake but the water began to get dirty. When he drank the dirty water he got dizzy, and hurt all over, and he could not recall anything that happened after that. Dorian says that what happened to him was probably a symptom of the dirty water. Gepyo then says he can't live here anymore because if the water gets dirty he'll become an even more terrible monster. He then wants to cleanse his body for a while, to which Dorian says to go to the spring in Taisai Square which is near the Mana House which should help him a lot.
He befriends Dorian after he saves him from the pollution overtaking the Taisai River. Dorian also gains access to the Mappa Woods and gets the Mound Super Magic spell and the ability to use Land Make.
Throwing Mana Drops into his pond at Woods Square will change them into different drops. His polluted form is the third boss in Eco-Creatures: Save the Forest.