Haruka Arimura, aged 30 and the eldest of four sisters, becomes head of the household after their mother disappears during a Paris trip and their father dies from grief. She sacrifices personal aspirations to raise her younger sisters, managing the household while navigating complex dynamics like youngest sister Fuyuko's lack of maternal memories and middle sister Natsuno's preoccupation with romance.

When a television news report features their mother as a mysterious Asian fashion designer in Paris, Haruka leads the sisters to France to find her. Discovering their mother has amnesia from a car accident and has bonded with a Frenchman's motherless daughter, Haruka chooses to leave her in Paris rather than use Junkers' final wish for immediate memory restoration. This decision reflects her empathy for the French child and desire not to disrupt the new emotional support system.

After returning to Japan without their mother, Haruka continues as household head. She dreams of their deceased father commending the sisters' maturity, reinforcing her choice to prioritize familial compassion over personal reunion.