The war between the Levamme Empire and the Amatsukami Imperium has been raging for years. In the midst of this struggle, the prince of the Levamme Empire declares his love for Juana del Moral and vows to end the war in one year, as part of his marriage proposal. When the Amatsukami catch wind of this, they assault the del Moral residence, targeting Juana's life. As a last ditch effort to bring the prince his bride, the San Maltilia Airforce hires a mercenary of mixed blood—a bestado—to fly Juana to the Levamme capital in secret. The pilot, Charles, accepts the mission...but traversing an ocean alone, into enemy territory, proves a much more dangerous ordeal than anyone could have anticipated.

In the far future, the elevated irradiation from the sun has destroyed the environment of the earth and the birthrate of humans has drastically decreased. The government controls society with an army of cloned soldiers called "Ideal Children (IC)". Sam Coyne is a trader in a desert. One day, he saves a beautiful woman Maya, who has been chased by Theseus, a corps of IC. He shelters her in his trade ship, but the destroyers of Theseus surround Sam and Maya.

Piano no Mori tells the story of Shuuhei Amamiya, a transfer student, and Kai Ichinose, a problem child from the rough areas of town. Upon transferring to Moriwaki Elementary and telling the other kids about his talent for piano, Shuuhei quickly finds himself as the victim of bully Daigaku Kanehira. Daigaku dares Shuuhei to find and play a cursed piano in the forest, which leads him to meet Kai, who claims to be the owner of the piano and the only one who can play it. Intrigued, Shuuhei follows Kai to the hidden piano in the forest and listens to him play a beautiful medley. Earning the respect of not only Shuuhei but school music teacher Sousuke Ajino as well, Kai now finds himself formally learning how to play the piano.

Apparitions, oddities, and gods continue to manifest around Koyomi Araragi and his close-knit group of friends: Tsubasa Hanekawa, the group's modest genius; Shinobu Oshino, the resident doughnut-loving vampire; athletic deviant Suruga Kanbaru; bite-happy spirit Mayoi Hachikuji; Koyomi's cute admirer Nadeko Sengoku; and Hitagi Senjougahara, Koyomi's eclectic girlfriend. A new semester has begun and with graduation looming over Koyomi, he must quickly decide the paths he will walk, as well as the relationships he will form and friends that he will save. But as strange events begin to unfold, Koyomi is nowhere to be found, and a vicious tiger apparition has appeared in his absence. Hanekawa has become its target, and she quickly finds she must fend for herself.