Chichi no Jikan follows Shinogi Kyuuichi, a male biology student living in an apartment near a friendly woman neighbor/friend, Takarai Ayaka. One day, aliens contact him, telling him to raise their child for a year … And maybe the entire universe is history. The infant is apparently female, and the way humans are raised is by breastfeeding. Kyuuichi ‘s sex is not a concern for aliens: they send him a simple gadget that transforms his body into a woman with a simple click of a button. Conveniently, the female form of Kyuuichi is very well endowed.
While she is naturally overwhelmed and uncomfortable with the whole thing, Ayaka helps Kyuuichi out as he navigates the unfamiliar process of raising a boy, and breastfeeding in particular. That includes going to a pharmacy to buy a breast pump, going to a maternity hospital to have a massage to unlock Kyuuichi ‘s accumulated milk, and giving the baby a bath together. Kyuuichi, a biology major, is intrigued by the whole thing.