Fourteen-year-old Iruma Suzuki has just been abandoned and sold to a demon by his irresponsible parents! Surprisingly, the next thing he knows he's living with the demon who has adopted him as his new grandson and has been transferred into a school in the Netherworld where his new demon grandfather works as the principal. Thus begins the cowardly Iruma-kun's extraordinary school life among the otherworldly as he faces his true self, takes on challenges, and rises to become someone great.

After swearing off music due to an incident at the middle school regional brass band competition, euphonist Kumiko Oumae enters high school hoping for a fresh start. As fate would have it, she ends up being surrounded by people with an interest in the high school brass band. Kumiko finds the motivation she needs to make music once more with the help of her bandmates, some of whom are new like novice tubist Hazuki Katou; veteran contrabassist Sapphire Kawashima; and band vice president and fellow euphonist Asuka Tanaka. Others are old friends, like Kumiko's childhood friend and hornist-turned-trombonist Shuuichi Tsukamoto, and trumpeter and bandmate from middle school, Reina Kousaka. However, in the band itself, chaos reigns supreme. Despite their intention to qualify for the national band competition, as they currently are, just competing in the local festival will be a challenge—unless the new band advisor Noboru Taki does something about it.

In 2012, after the events of Digimon Adventure: Last Evolution Kizuna, the early adulthood DigiDestined—Daisuke, Miyako, Iori, Takeru Takashi, Hikari, and Ken—must reconcile their new responsibilities with their Digimon partners. But Rui Owada, a mysterious young man, appears, claiming to be the first human to partner with a Digimon–Ukkomon. Could Rui really have been the first-ever DigiDestined?