In the near future when technology has significantly advanced, a famous AI TV fortune teller seemingly foresees high school student Asahi Kashiwagi's day with pinpoint accuracy. On his way to school, he encounters Aoi Izumisawa, Bai Mongfa, Karin Istel, Amelia Irving, and Ilya Ilyukhin. Despite meeting them for the first time, Asahi suddenly receives love confessions from all of them at the end of the same day, perfectly aligning with the fortune teller's prediction. As if that was not enough, Asahi soon learns that these five individuals are actually candidates to become his bride, and they have been invited by his father to live at Asahi's home. Left with no other choice, he reluctantly allows them to stay, resulting in a bawdy turn of events that brightens up his average high school life. However, as Asahi spends more time with them, forgotten memories gradually resurface. While uncovering the hidden truth, Asahi begins to believe that his fate with these potential partners might be more than just mere coincidence.

Third-year high school student Jirou Yakuin is in love with his childhood friend and classmate, Shiori Sakurazaka. Thus, he hopes to be paired with her for the marriage practical: their school's practice of randomly selecting boy-girl pairs to live as pretend married couples while monitoring and rating them on how close they have gotten. Meanwhile, the lively Akari Watanabe wants to be assigned to her crush, the popular and good-looking Minami Tenjin. Much to their dismay, Jirou and Akari find out that not only have they been paired together, but so have Shiori and Minami! Determined to be with their crushes, Jirou and Akari strive to earn as many points as possible, as the top 10 pairs earn the right to switch their partners—so long as both couples agree.

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.

To the shy and reclusive Ryuuto Kashima, associating himself with his popular classmate Runa Shirakawa is nothing but a distant fantasy—or so he thought. After losing a bet with his friends and being coerced into confessing to Runa, Ryuuto's world is flipped upside down: instead of the cruel rejection he was expecting, Runa agrees to go out with him! But dating Runa proves to be overwhelming for Ryuuto, who requests that their relationship remain a secret known only by their closest friends. His decision, however, leads to a series of mishaps that he fears will doom the relationship. As they work through their misunderstandings, Ryuuto reveals his insecurities stemming from his past experiences, and the two grow closer together. Just when things are getting back on track, Ryuuto's middle school crush, Maria Kurose, transfers to his class and begins to stir up a fuss. At the same time, terrible rumors about Runa spread around the school, prompting Ryuuto to take desperate measures to protect her.