A 19-year-old housekeeper named Muku responds to a live-in help wanted ad and arrives at a decaying mansion in the Itabashi district that locals have nicknamed the "devil's mansion." The crumbling interior is unnerving, but the property hides a breathtakingly beautiful garden that seems out of place with the rest of the building. Strange, eerie screams occasionally echo from within the walls, feeding the rumors that surround the house. Muku discovers that the mansion is home to three sisters who together run a global fashion brand. Each sister possesses a specialized skill—design, tailoring, or business—and together they maintain their family's atelier behind the mansion's closed doors. The sisters are reclusive and their lifestyle is far removed from the outside world, which keeps them dependent on one another and suspicious of strangers. Muku, a calm and quietly competent young man who simply focuses on doing his job well, gradually wins their trust through his steady presence, cooking, and domestic care. The story follows the daily life of this unlikely household as the housekeeper navigates the sisters' eccentricities, helps them with challenges both mundane and professional, and slowly draws out the secrets that have kept the mansion sealed off from the world. The first major narrative arc centers on the eldest sister, Hikaru, a reclusive designer who struggles with agoraphobia and must venture outside for the first time in years when a close friend commissions a dress that requires her to revisit a meaningful childhood location. Later arcs deepen the relationships among the four residents, revealing the personal histories and unresolved grief that led the sisters to isolate themselves, and showing how Muku's unwavering support encourages them to reconnect with the world.