The "Oniichan Making System" (OMS) allows players to define their character's persona, which influences how their sister and other guild members perceive them. Expansion DLC and Updates Living With Sister: Monochrome Fantasy - Steam Community

The v2.0.0 update introduced the refined system, significantly deepening character interactions.

Evenings are dedicated to household management and bonding. Players must manage finances, cook meals, and monitor their sister's health, which is central to the game's progression.

The story follows a young man who must balance his dreams of becoming a legendary adventurer with the pressing responsibility of caring for his sickly younger sister. Following their father's departure, the protagonist joins the local to earn money through odd jobs and monster hunts.

Trust and interest are core metrics. Players start with a "pure sibling bond" that can evolve through various stages, including "Curious," "Sexually Open," and "Degenerates," depending on player choices and dialogue.