The story follows Sanada Yuki, an energetic and proactive commoner boy who helps his mother run a bicycle shop, and Tenkoin Junna, a sheltered heiress from one of Japan's most powerful financial conglomerates. Yuki attends a classical piano concert with his mother, where Junna performs. Afterwards, he discovers Junna alone on the streets, having run away from her restrictive life lacking freedom, and rescues her from being harassed by men.

Yuki empathizes with her situation and decides to become a friend for the day, taking her on an impromptu adventure. He buys her a notebook and advises her to write down one hundred things she wants to do, promising they will accomplish them together. This starts with Junna expressing a desire to fly, leading them to a theme park to try a bungee jump. When Junna's maid, Chikage, eventually arrives to take her home, Yuki boldly declares, even though they just met, that he already likes her.

Refusing to let their connection end, Yuki confronts Junna's father, Haruomi, and vows to earn the right to stay by her side. He sets an immense challenge for himself: to gain admission to the prestigious elite school Junna attends, the Kokitei Academy. More than just passing, Yuki aims to place at the top of the entrance exams to prove himself worthy despite his commoner status. The father reluctantly agrees under strict conditions, and Chikage is assigned to supervise their limited interactions.

The narrative focuses on Yuki studying relentlessly while navigating the class difference and the obstacles placed before them. He takes Junna on chaperoned dates to continue checking off their list of one hundred dreams, fostering a genuine bond. A key arc involves a New Year's shrine visit where a theft incident forces Yuki to protect Junna, resulting in an injury that jeopardizes his entrance exams. With Junna's emotional support and a grudgingly given push from Chikage, Yuki perseveres, ultimately passing the exam and officially becoming Junna's boyfriend. The series follows their ongoing relationship from that starting line, exploring how they overcome the social gap, deal with parental opposition, and continue to fulfill the wishes recorded in the notebook, all while Junna gradually learns about the ordinary world and Yuki demonstrates that his life experience and hidden talents make him more than an ordinary commoner.