Is Maria coming back?

Sora, the third of four sisters, inherits from her father Sakamoto Medical Practice in Kabukicho, Shinjuku. Sora sees even those with no money and the waiting room is always crowded penniless patients. Keeping the indebted surgery going is tough but Sora manages to carry on with a smile and becomes a popular figure in the neighbourhood.

The oldest sister, Umi, is a single doctor researching gene therapy. The second sister, Riku, is the wife of the owner of a large hospital. The fourth sister, Mimi, is a trainee doctor dreaming of becoming famous. The four of them have very different stances on what it means to be a doctor, assuring that every gathering results in a fraternal fight.

One day, Umi calls the four sisters together and introduces them to a young girl they have never seen before. It turns out to be Hiyo their heretofore unknown half-sister from Hokkaido. Hiyo is very sick, her body being invaded by a heavy illness.