If you're looking for manga similar to 15-sai, you might like these titles.
Being a teenage girl is not easy. Mari, a high school girl, struggles to find her place amongst the common sociological beliefs. Stigma, prejudice, and discrimination has seeded doubt and stress in Mari as her identity is being challenged. This story is created in support of LGBT teens who face social challenges and negative attitudes from society, the innate struggles of adolescence are further complicated leading to the potential development of mental health concerns. Now - Mari is trying to overcome the stigma.
Back in high school Sono confessed her love to Sato, but she was turned down. Now she lives as a freeloader in an apartment shared with her girlfriend, Hiroko. However, she still hasn't forgotten about Sato and when she cries out her name while having sex with Hiroko, she finds herself in some serious trouble...
Shimada Asami has always been doing as she's told: following the prescribed path. Though she loves playing the piano, she goes to a regular college instead of a conservatory, and in the same manner, Shimada's actions always fall within people's expectations without her ever kicking up a fuss. However, when a childhood friend reveals further intentions, Shimada becomes close to a female co-worker, and her life begins to change.
When she was young, Yukino Miyashita wanted, more than anything else to become an idol. After accomplishing her dream, however, the idol group she was part of failed to sell, and she returned to school, facing alienation from her peers. Now, at age 18, Yukino is living alone in Tokyo, half-heartedly trying to start a new life as a talent manager, while not quite able to put her idol days behind her. She meets Setsuko, a songwriter who also once belonged to a failed idol group. The romance sparked by her encounter with Setsuko causes Yukino to reevaluate her own life.
Rutsu, a novelist, finds herself caught between her boyfriend and another woman.
Kaburagi Aya, a highschool student who is at the bottom of the school caste, and Kurosaki Sei, a teacher who was oppressed by a trauma from the past, get to know each other through a dating app. With ulterior motives from both sides, the relationship between them gets distorted gradually...
Follows Ayu Shirakawa, who has run away from home. Through her cousin Miyako, Ayu is introduced to the author Yukari Ebiwara (penname Hikari Ebiwara), and starts a part time job as her caretaker. Yukari often slacks off by playing games and going on trips, but Ayu really enjoys her new everyday life. And as the two live together and grow closer, Ayu starts to have feelings she never had before.
Kyouko, a university student, is in love with her best friend Masumi, and is getting to the point where she can't stand it any more. Cue alcohol.