The game follows a young Cloak Figure named Lui who finds herself in a forest-like world called the Maulands with no memory whatsoever of how she got there. When she is attacked by some mysterious shadow-like wolves, Lui wakes up in an infirmary of a small town named Canopy Village and is given a home at Macara's Foster Hut. She meets Rocky and Freyo, slowly adapting to the place.
On the fifth day of staying in the foster home, she and the other fosters travel in the Talent Train to the Talent Show in Neosun City. When they arrive, Lui realizes that there are others like her and decides to investigate with her friends after the show. Unfortunately, halfway through their act, the show is interrupted as a black corruption fills the room with darkness.
Impure plays like a normal 2D side-scroller platformer, with a sketchy chibi style and mostly dim area with an aura of light around the player. There are also Safe Areas. Entering a town or other Safe Area, the name of that area would appear above. Enemies cannot enter nor attack the player in a Safe Area, due to an invisible barrier, with the exception of Neosun City when it's attacked.
NPCs can appear in both Safe Areas and normal areas. The player can talk to them and give choices to ask or talk about. Sometimes the player will learn a fact about the NPC and will add to their Journal as part of the NPC Log, just incase the player needs it later. That way, the player can use that information for later instances.
The journal is first given to the player by Macara at the near end of Day One. It can been seen in the player menu, alongside the inventory, equipment, buffs, stats, and currently unlocked skills. It would consist of an NPC log, past memories, the player's saves, and pages that each get filled after a day.
Skills are first introduced in the middle of Day One's skill class. They are unlocked for a certain goal or currency, and can be equipped by the player to suit their play style. Each skill offers an ability to the player, set in three categories: melee, ranged, elemental, effective, and special. The player's first skill can be chosen between four elementals, resembling fire, water, earth, and electricity.