Teru Kurebayashi is left completely alone after the death of her older brother, Souichirou, her only remaining family member. Before he died, he gave her a cell phone containing the contact information for a mysterious and anonymous figure who calls himself Daisy. Through text messages, Daisy becomes Teru’s emotional anchor, offering encouragement, advice, and companionship as she navigates her lonely daily life. She has never seen his face and knows nothing about him, but she grows deeply dependent on his messages.

One day, after bullies from the student council are inexplicably driven away, Teru accidentally breaks a school window. Unable to pay for the damage, she is forced to work for the school’s gruff, ill-tempered janitor, Tasuku Kurosaki. Kurosaki appears to be a lazy, rude, and sharp-tongued twenty-four-year-old who enjoys ordering her around. Despite his abrasive exterior, he secretly watches over her with a quiet protectiveness that she does not understand. As Teru spends more time with Kurosaki, she begins to notice strange coincidences: the timing and content of Daisy’s messages often align with Kurosaki’s actions. She starts to suspect that the janitor might be the very person she has been confiding in all along.

The central mystery of the series revolves around Daisy’s true identity and Kurosaki’s hidden past. Kurosaki carries a heavy burden of guilt, believing that his own actions indirectly caused Souichirou’s death. This belief prevents him from openly returning the feelings that develop between him and Teru, even as their relationship deepens. Alongside the romantic tension, the story weaves in elements of suspense and conspiracy involving hackers, corporate secrets, and dangerous figures from Kurosaki’s former life. Teru’s unwavering trust in Daisy and her growing bond with Kurosaki drive her to uncover the truth, while Kurosaki struggles to protect her without revealing his secrets. The narrative balances lighthearted comedic moments with intense emotional conflicts, exploring themes of grief, guilt, loyalty, and the quiet courage found in caring for someone from the shadows.