Io was inspired by Hayao Miyazaki's Princess Mononoke, Neil Gaiman's The Sandman: The Dream Hunters, Moon Studios' Ori and the Blind Forest, Clover Studios' Okami, Ubisoft's Child of Light, and E-Line Media's Never Alone. It started out simply as a desire to create a 2D sidescrolling platformer featuring a shapeshifting fox spirit.

In early iterations, the forest was becoming corrupted due to the presence of poachers. Io was meant to free animals from their traps lest they become corrupted spirits. The current iteration has done away with the poachers but retained a forest slowly falling to corruption, trapping its inhabitants.

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Each level is based on a time of day: First Light, Sun's Zenith, Sun's Descent, Last Light, and Ember Night. They also correspond to which skills and shapeshifting ability you will learn. First Light is Io's awakening as a forest spirit and the fox guardian will help her get started in a forest environment. Sun's Zenith features the badger guardian and the deep part of the forest features several areas to dig through in Io's new badger form. Sun's Descent bring Io to a more water filled area where she meets the beaver guardian. Last Light is when the owl guardian appears to Io allowing her short bursts of flight in her newly acquired form. In Ember Night a fire rages, forcing Io to use all her abilities to save the forest, allowing her to become a forest guardian.

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