Imagine being the only child your whole life, and then suddenly finding yourself gaining 13 step-brothers! Ema Hinata's lonely life takes a new and exciting turn when her single father Rintarou Hinata, a famous adventurer, falls in love and marries Miwa Asahina, an apparel maker. In order to give the newly-wed couple space, Ema starts living with her new step-brothers in a mansion called Sunrise Residence and for the first time, experiences being part of a lively and big family. She finally feels safe and content. Each brother has his own unique personality, and Ema soon realizes that it is not only family love that grows between them, but romance as well. Which brother will be the one to steal her heart in the end?

For high school students like Shouichi Kamita, university entrance exams and the future are common concerns. It is also during this time in life that a mysterious emotion that vexes people of all ages may begin to weigh upon one's mind—love. At this point in his teenage years, Shouichi finds three girls he could see himself having a future with: the ever-cheerful Hikari Tsuneki, who teases Shouichi without mercy, but actually has a softer side; the competitive gamer, Tooru Miyamae, who has difficulty communicating with others; and Shouichi's childhood friend, Kyouko Touno, the sometimes immature shoujo manga enthusiast. Seiren follows Shouichi's relationships with these three girls across three separate arcs, as their feelings grow from mutual interest and blossom into something more beautiful.

High school girl Maika Sakuranomiya has trouble finding a part-time job because of how scary she looks when smiling. However, she is scouted one day by Dino, the manager of the café Stile where its waitresses play unique traits such as tsundere and younger sister. Maika is given a sadist trait because of her looks and has to adopt a dominant and cruel persona when servicing customers, particularly masochist ones.