One day, a fourth grader called Yuuta Tomonaga stumbles upon the police's new project, a sentient police robot called Deckerd. Soon after he visits Deckerd several times and teaches him various things about life, Deckerd's AI becomes self-aware and he begins to develop a "heart". But the day comes when he is to be sent into action, and the police prepare to wipe his memory, which includes his friendship with Yuuta. Yuuta tries to stop the wipe but is unsuccessful.