After Keita Suminoe's mother passed away, his father promptly remarried, introducing two step-sisters into Keita's life: twins Ako and Riko. But since their fateful first encounter, a surge of incestuous love for their younger brother overcame the girls, beginning a lifelong feud for his heart. Now at the end of his middle school career, Keita studies fervently to be able to attend Ako and Riko's high school. While doing so however, he must resolve his conflicting feelings for his siblings and either reject or succumb to his sisters' intimate advances. Fortunately—or perhaps unfortunately for Keita—his sisters aren't the only women lusting after him, and there's no telling when the allure of temptation will get the better of the boy as well.

Haruka and Sora Kasugano are coming home, to a place filled with memories. Having lost their parents in a tragic car accident, the twins resolve to return to the countryside and start life anew at their grandfather's house, the haunt a constant reminder of moments from their past. Greeting them are childhood friends Nao Yorihime and Akira Amatsume, and newcomer Kazuha Migiwa. It is a warm welcome, symbolic of the days that should come. Their peace is merely ephemeral, however, as suppressed emotions, born from vows both newfound and forgotten, start exerting their influence on the twins' new lives. And deep down, a dark secret, only known to them, begins to unshackle. Based on the visual novel by Sphere, Yosuga no Sora not only explores the power of lost memories and true love when the bonds of many become intertwined, but also raises the questions of morality and social acceptance.

Tetsuhiro Morinaga is in love with his upperclassman Souichi Tatsumi. He even manages to confess his love. Too bad it turns out that Tatsumi is an aggressive, self-centered, and outspoken homophobe. Yet somehow Tetsuhiro managed to fall in love with Tatsumi, the “walking personality disorder,” who is the kind of man who declares that all gay men should be wiped off the face of the planet. An unfortunate accident with an aphrodisiac drug brings the two men physically together against Souichi’s will. The experience has a life-changing effect on both men. But will it ultimately bring them closer, or drive them apart?

A sequel to Aki-Sora under a new name.