Mercurius Pretty is a "raising simulation" game, similar in concept to Princess Maker games, but without their RPG elements (exploration, combat, etc.). The player is entrusted with the task of raising a "homunculus", a female fairy-like creature who has to grow up as a human in a medieval fantasy world. The player selects a schedule for the homunculus every day. Each activities raises a certain attribute by a number of points. For example, praying increases spirituality, reading books increases knowledge, etc. The goal is to raise attributes selectively and pass exams, putting the homunculus on one of the various paths (spiritual, combat- or magic-related, and so on).
The homunculus' mood decreases when studying; it can be normally increased by talking to her. Different approaches (praising, scolding, etc.) may result in a positive or negative effect, depending on the himunculus' initial state (normal, sad, angry, and so on). The homunculus will also get sick from time to time and require rest. It is possible to buy books and crystals, which may greatly increase the homunculus' corresponding attributes. After a number of days, the homunculus will change her shape, turning into a more human, grown-up person.