Primal tells the story of Jennifer Tate, a 21-year-old woman searching for her boyfriend through a series of demonic realms. As the story develops, more is revealed about Jen's past and her relationship with her boyfriend, as well as the nature of the demon worlds.

In Primal, the player can control either Jen or Scree as they navigate the realms of Oblivion. As the game progresses, newer demonic forms are obtained, which prove invaluable in solving various puzzles and combat.

Control can be switched between Jen and Scree at any time in game. When in control of one, the other will be operated by AI, performing various functions depending on the situation. During play, the characters can interact with one another, performing actions such as asking questions, or siphoning energy.

When in control of Jen, the player may transform into one of four demonic forms for various purposes, depending on the situation (provided the forms are unlocked). When in a demon form, Jen experiences a boost in attack, defense, speed, attack range and access to abilities unavailable in a human form. The tattoo on Jen's back also glows when in a demon form, corresponding to various forms.

Defeating enemies involves weakening enemies to the point where their hit points reach zero, at which time a finishing move must be performed to kill the enemy. While the moves differ in style and time taken, the final effect remains the same. Enemies can be finished off before the health bar reaches zero, and doing so leaves more residual energy.

While Jen can remain in a demonic form indefinitely, taking damage will reduce health. However, hit points here are represented by demonic energy. When an enemy is killed, the remaining energy can be drained through use of Scree, who can store the energy for when it is needed. Jen can then call on the energy, siphoning it off to replenish her own. Scree can store a vast amount of energy, but also has limits as to how much.