Kaho Nikaidou, a freshman from a prestigious family, escapes the sheltered world where no one dares criticize her by moving into a dormitory for a fresh start. One day, she is rescued from a reckless move in traffic by a blunt yet attractive stranger named Kanade Takahashi, who challenges her like no one else has. Intrigued by his honesty, Kaho falls for him, only to be stunned by his unexpected secret - he's just a fifth grader. Despite her initial intentions to end the relationship, Kaho finds herself drawn to Kanade's genuine and caring nature, leading her into a unique romance with her much younger boyfriend in Hatsukoi Monster.