When Kasumi Toyama was out camping as a child, she heard the rhythm of the "Star Beat" while admiring the starry night sky. This sparkling, heart-pounding sound left a lasting impression on her, and since then, she has constantly been seeking to rediscover that exciting thrill. Now, as a newly enrolled student of Hanasakigawa Girls' High School, Kasumi is more determined than ever to find that long-lost sensation again. She attempts a myriad of school club activities, and even considers taking up a part-time job, but none of these feel suitable for her. That is, until she chances upon a star-shaped guitar in the storage room of an old pawn shop. It leads her to a live house, where she is captivated by watching a live performance for the first time. Spurred from the adrenaline, she instantly decides to form a band without even really knowing why. However, such a venture requires her to confront various hurdles with new friends she makes along the way, all in her pursuit to encounter that twinkling, heart-throbbing ardor once more.

In 1931, the Tokugawa Shogunate remains in power, marking the 64th year of the Meiji era. Holding a monopoly over the newly discovered "Dragon Vein," the government is leading Japan toward an advanced Edo period. During this time, an elite force of executioners called "Nue" is tasked with defending the Shogunate from a rebel institution known as the "Kuchinawa." As the owner of the Tsuyukasa Bookshop, Sawa Yukimura runs the store's day-to-day business inconspicuously. But behind the scenes, she seeks vengeance against the man who slaughtered her tribe and family. With a special ability to transform granted by her blue blood, Sawa joins Nue after being promised information regarding the target of her revenge: Janome, the leader of the Kuchinawa.

Life is not going well for 28-year-old Kyouya Hashiba. Having left his office job to pursue a career in the video game industry, his internship at a popular game studio abruptly ends, leaving him unemployed and forcing him to move back in with his parents. Additionally, his jealousy toward the success of the "Platinum Generation"—a group of similarly-aged creators—has caused him to regret his decision to attend a traditional university instead of an arts college. Even though he believes there are no second chances in life, Kyouya is suddenly given one when he wakes up one day and finds himself 10 years in the past. Instead of choosing business school like he originally had, Kyouya decides to pursue his passions and attends the Oonaka University of Art. There, he meets classmate Eiko Kawasegawa, the woman who had hired him as an intern in the present, alongside his new housemates and future Platinum Generation members: underachieving artist Aki Shino, aspiring singer and actress Nanako Kogure, and naturally-gifted writer Tsurayuki Rokuonji. With each project they complete together, Kyouya and his friends venture closer to discovering their true potential as creators and remaking their lives into the ideal versions they desire.

Ancient Japan is under attack by powerful beings called "Kamikui," and it is up to the "Oni" and his band of eight beautiful female warriors to stop them. Each of these girls have unique skills, abilities, and personalities. They partner themselves with the Oni, Jin, to stop the miasma of darkness sweeping across Japan. Onigiri follows the escapades of Jin and his merry companions as they strengthen their bonds and fend off the demonic invasion.