Monotone Princess is an action game based on the Soul Eater manga. As many people disappearances have been reported, the Shinigami school Shibusen's teachers decided to send their top students investigate. Masked creatures are gathering souls, and unlike Shibusen's Meisters and Weapons, they are not consuming these souls as they are captured, but are planning to use them for another purpose.

The player controls a Meister, either Maka, Black Star or Death the Kid, accompanied by their Weapon partner to fight those masked creatures. The game is separated in a number of missions leading to a boss fight. A number of foes, displayed in the lower-right corner, must be found and defeated in each stage. While exploring, the Weapon follows the Meister in human form, and changes into a weapon when enemies are encountered. Health is replenished by sun icons found by breaking crates lying around during exploration phases. Once the target number of defeated foes is reached, the level is cleared, and the player is rated on clear time, damage taken, number of hits and level bonus. The next mission can then be selected.