One Monday morning, a high school girl named Ai who meets with a salaryman at a train station every Monday morning. The man somewhat acts as Ai's bodyguard, who protects her from the other passengers aboard the crowded train.
One Monday morning, the Salaryman is getting scolded by his Chief Manager for not able to satisfy his quota. After seeing a pamphlet of a gym named Tawawa Sports, he opted to visit. Later in Sunday, a trainer at Tawawa Sports coaches a man who seems to be tired with his works, as well as giving advice that "result isn't everything, the progress is". The office worker is revealed to be the Chief Manager, while Salaryman himself stating to Ai that he's too lazy to go to gym.
A female employee asks if Junior wants to go on a blind date. When she refuses, the female employee mentions Junior's ex-boyfriend in front of the Senior. After a drinking party, Senior carries the drunk Junior on his back afterwards. However, while Senior carries Junior to her apartment, Junior reveals that she actually has no boyfriend from her hometown at all, and that she uses this lie to avoid any possible romantic advances from other men.
One Monday morning in Summer, Ai tells Salaryman that she's going to spend her summer vacation with her cool and popular best friend while Salaryman complains that unlike students, workers barely get a day off.
One Monday morning, Salaryman visits Ai-chan at her part-time job as a waitress at a bakery. She arranges for a meeting afterwards and decides to give him her waitress uniform with some buttons off.
One Monday morning, Ai is having trouble while running at the school's marathon activity, and is confused with why her friend, who also has fairly large breasts, seems to be not bothered after running for a long time.
One Monday morning, an office worker attends his junior high school reunion and meets a woman whom he missed his 'chance' with back in their student days.
One Monday morning, Salaryman asked what Ai did during the Christmas day, which she initially refuses to answer. Later, she revealed that she 'has taken a step into adulthood', becoming from 'I-chan' to 'J-chan'.
