Just Because!

After middle school, with its bullying and nicknames, Uka Ishimori is excited for a fresh start at Hachimitsu High School. Kai Miura, a cool and uninhibited boy, sits next to her in class. Uka remembers she met Kai in middle school and with a single word, he had convinced her to attend Hachimitsu. Though he’s popular, Kai supports Uka in her efforts to fit in with her new classmates.

Nanami Takahashi is a high school student entering her first year. Immediately on her first day however, she becomes the victim of a practical joke by the school's most popular guy, Motoharu Yano, who coincidentally also ends up in her class.

In a futuristic society, Japan has implemented a complex system referred to as "The Red Threads of Science" to encourage successful marriages and combat increasingly low birthrates. Based on a compatibility calculation, young people at the age of 16 are assigned marriage partners by the government, with severe repercussions awaiting those who disobey the arrangement. For Yukari Nejima, a teen that considers himself average in every way, this system might be his best shot at living a fulfilling life. However, spurred by his infatuation for his classmate and long-time crush, Misaki Takasaki, Yukari defies the system and confesses his love. After some initial reluctance, Misaki reciprocates his feelings in a moment of passion. Unfortunately, before the two can further their relationship, Yukari receives his marriage notice. He is then thrown into a confusing web of love and lies when his less-than-thrilled assigned partner, Ririna Sanada, becomes fascinated with his illicit romance.

When the intimidating Rintaro meets the open-minded Kaoruko, the unlikely duo grows closer. The issue? Their neighboring high schools hate each other.

Banri Tada is a freshman at a Tokyo law school. After an accident, he suffers severe memory loss. Despite the incident, he befriends fellow freshman, Mitsuo Yanagisawa, which leads him to the beautiful, yet obsessive, Kouko Kaga.

Shuichi Nitori transfers to a new elementary school, and there, meets Yoshino Takatsuki. The two children discover they share a similar secret.

For Makoto Hanaoka, life’s about to get more complicated. Saki Aoi, a lively girl with loads of confidence, confesses her love for Makoto one day. When he fails to reciprocate, Saki declares she will be his first love! She shares her goal with a mutual friend, Ryuji Taiga, who also confesses his crush on Makoto. Stuck in a love triangle, Makoto must find a way to make it work and have fun.

Shinichiro is a student living in what would be a dream come true for most high school boys, but for him is mostly a frustration. A well liked girl in school named Hiromi has lived in his house for a year along with his family. Her father was a close friend of the family, and when he died they immediately took her in. She is popular and well liked, always smiles, is talented in sports- but Shinichiro knows there must be tears inside her. Having an artistic tendency, he makes watercolours of her and thinks about wishing to ease her tears. Yet he cannot bring up the nerve to talk to her even in his own home. She, too, is quiet and withdrawn in their house, quite unlike at school. Shinichiro is also distracted by teasing from his friend Nobuse for watching Hiromi from afar, a curse of bad luck from a strange girl named Noe, and being forced to perform Muhiga dancing. By helping Noe he hopes to ease his own problems, yet he seems to have difficulty helping himself.

Yuki Takeya, Kurumi Ebisuzawa, Yuri Wakasa, and Miki Naoki decide to stay over at school. Along with the school adviser Megumi Sakura, they suddenly find themselves to be the final survivors of a zombie attack, and continue to live and survive at the school.