Heart energy, in its own way, is like a currency in Shining Hearts. You can earn it many ways, by talking to people, clearing quests, and fighting monsters. Defeat a monster and the neighboring monsters may express their sadness by releasing blue hearts or anger with yellow hearts.
You can also spend heart energy in many ways like baking bread and picking conversation choices. This communication trailer from Sega demonstrates the system and secret night events with the game’s heroines, which act like date scenes.