Amamiya Goro, an obstetrician-gynecologist practicing in a remote region of Japan, led a simple, uneventful life—until one day, the arrival of a particular patient completely upended his world. That patient was none other than his idol, Hoshino Ai, the eternal center of the pop group B-Komachi, affectionately nicknamed "Ai." She was pregnant with twins and planned to give birth in secret. Shocked by the situation, Goro resolved to support her wholeheartedly. However, just as Ai was about to deliver her babies, tragedy struck—Goro was fatally attacked.

When he opened his eyes again, Goro discovered to his astonishment that he had been reincarnated as Hoshino Aqua, one of Ai's newborn twins. Though bewildered by his new reality, his admiration for Ai remained intact. Alongside his twin sister Ruby, who had also undergone reincarnation, Aqua took on the role of supporting Ai as family.

Ai kept the secret of her underground childbirth hidden and continued to focus on her idol career. Her efforts paid off spectacularly as her popularity soared, culminating in B-Komachi's long-awaited concert at Tokyo Dome. But on the morning of this monumental event, tragedy struck once more. Ai was brutally stabbed at home by a stalker and succumbed to her injuries before the eyes of Aqua and Ruby.