The Taisai River is a location in Mana Woods. Dorian goes there after fighting Garbage Monster Sludge after he realized the water may have been dirty and polluted. The Kingdom activated a dirty water extruded on top of the river. When he comes there he finds out the river was polluted with dirty brown water. However the water used to be clean and taste good. He finds hurt Ecoby and fixes them up. Dorian finds the river and can now go to the river. He also gains access to the wireless battles, and a new Super Magic spell, Downpour.
Dorian destroys a machine and then tells two more to stop dirtying the river. The machines then run away and then asks the Wood Spirits to ask Master on how to clean it. He figured out that he can see what's causing it while he learns how to clean the river.
Dorian discovers a dam in the Taisai River that is causing a blockage of water from entering into the rest of the river. He thinks that all that water is used for the Kingdom's animals, and figures that the dirty river water is coming from somewhere else as the water at the dam is extremely clean.