After graduating from high school, Mai Kawai's top priority was to find a job with a stable income to avoid turning out like her father. However, despite having taken a variety of civil service exams, she was faced with a harsh reality: nearly every institute denied her entry. The only place that accepted her was a police academy, which she reluctantly joined. Even now that she is an actual police officer, the world continues to be cruel to Mai. Due to her profession, she unexpectedly receives constant criticism from disgruntled citizens. Disheartened by the hostile treatment, she decides to submit a letter of resignation after just a few months of employment. But on the same day Mai chooses to quit, she meets Seiko Fuji—the former ace of the Criminal Affairs Division who is assigned as her new instructor. Finding her new coworker to be enchanting, Mai delays leaving and gives her uninspiring job a second chance.

Although the city of Fukuoka might look relatively peaceful at first glance, in actuality it houses a thriving mixture of dangerous individuals such as killers, detectives, and professional revenge seekers right beneath its surface. Among their number is Zenji Banba, a laidback and observant detective who is investigating the work of other hitmen companies in the area. However, Banba might not be the only one with a bone to pick with these organizations, as Xianming Lin, a crossdressing male hitman in the employ of one such company begins getting fed up with his lack of jobs and pay. One day, after Lin's current target commits suicide before the hitman could reach him, his company refuses to pay him even half the amount they were originally supposed to for the assassination. Frustrated, Lin requests another mission and is offered the job of taking out Banba, whom his organization believes has been interfering with their business. However, when Banba arrives at his home and finds the hitman inside, Lin surprisingly doesn't even attempt to kill him. Instead, he offers the detective another option: to join him and form a team. With the offer on the table, exactly how will Banba respond, and just what plans does Lin have in store for the underground world of Fukuoka?

Following a prank pulled by his perverse friends, Junichi Hashiba asks a gal out in an attempt to change the fact that he's a hopeless virgin. Yukana Yame, the girl in question, is disgusted by Junichi's groveling. However, through a series of teasing remarks, she soon finds herself bonding with him and ultimately accepting Junichi's confession, much to his surprise. Hajimete no Gal follows Junichi as he overcomes his lack of self-confidence and suppresses his sexual urges, all while thrust into a whole new school life full of lively girls and unpredictable mayhem.

It is the day of the school festival, and Junichi Hashiba and Yukana Yame's class cafe is doing well. During a break from her shift, Yukana hears an urban legend about the festival’s after-party. According to the tale, couples who share the last dance together will be lovers for the rest of their lives. Unfortunately, others catch on to this rumor and decide to separate Junichi and Yukana before they can dance. Will the two be able to stick together, or will someone else whisk them apart?