Despite their age difference, the protagonist, Tetsurou Kitami, had a young girl named Sumire Nagayama living next door. Their relationship was almost like siblings due to their close neighborhood ties. However, due to her parents' job, Sumire had to move away, leading to a period of separation from Tetsurou. At their farewell, Sumire kept the promise she made with Tetsurou close to her heart and never forgot about reuniting with him, not even for a moment. Years later, Sumire, upon entering high school, moves into Tetsurou's house. She had longed for this moment immensely. Meanwhile, Tetsurou, having become unemployed, returns to his family home. The disappointment he felt at this time was unfathomable. Despite the gap in their feelings, the two reunite. "Welcome back, Onii-chan! Do you want dinner? Or me? Or... right here?" As if to make up for the time they were apart, their romantic relationship, despite the age difference, rapidly progresses without a hint of disparity in their emotions.