Biomutant has branching storylines where decisions made by the player will decide how the story will continue. The main plot revolves around the "Tree of Life", which is struck by a natural disaster and becomes polluted by poisonous oil from beneath the soil. The five roots of the Tree, through which it gives life to the whole world, also come under threat from five creatures who begin slowly gnawing at them, threatening to kill the Tree before it can heal itself.