A 5000-year-old vegan dragon was living peacefully when one day a young girl showed up in his cave. She offered herself as a sacrifice in order to gain favor for her village. He played along as the great "Evil Dragon, the Demon Lord's Army Leader" in order to get rid of her. However, his little white lie awoke her hidden powers and his peaceful life suddenly ended.

Daikichi Kawachi is a 30-year-old bachelor working a respectable job but otherwise wandering aimlessly through life. When his grandfather suddenly passes away, he returns to the family home to pay his respects. Upon arriving at the house, he meets a mysterious young girl named Rin who, to Daikichi’s astonishment, is his grandfather's illegitimate daughter! The shy and unapproachable girl is deemed an embarrassment to the family, and finds herself ostracized by her father's relatives, all of them refusing to take care of her in the wake of his death. Daikichi, angered by their coldness towards Rin, announces that he will take her in—despite the fact that he is a young, single man with no prior childcare experience. Usagi Drop is the story of Daikichi's journey through fatherhood as he raises Rin with his gentle and affectionate nature, as well as an exploration of the warmth and interdependence that are at the heart of a happy, close-knit family. [Written by MAL Rewrite]

Koro-sensei reminisces about his first meeting with Karasuma, where they first butted heads and fought against each other, ultimately coming to respect one another. However, Karasuma eventually points out their actual meeting wasn't nearly as eventful.