The entire universe is divided into the inner universe and the outer universe. The two universes are enemies of each other. The outer universe is ruled by demons, and the inner universe is divided into The Realm of gods, the Eternal Realm, and the Mortal Realm. In the universe, there are countless mortal worlds like the Tianfa Continent, and they are collectively referred to as the Jiutian Xin Region. In the field of Jiutian Xin, nine immortal emperors commanded all star fields in nine layers. Above the nine heavens is the realm of purification of immortal gods.

Welcome to the fascinating world of Gensokyo, in which youkai (A term for all sorts of spiritual creatures), animals and some humans live, completely separated from our world by a magical barrier. The only gateway between the two worlds is the Hakurei shrine. Reimu Hakurei is the maiden working at said shrine. Whenever problems of supernatural causes (known as "Incidents") occur, Reimu goes out with her friends to investigate, eliminate the cause and hopefully restore Gensokyo to its equilibrium.

Two and a half years have passed since the Lost July incident, a catastrophe that reduced an entire city to ruins and sent shockwaves across the world. On the desert planet of No Man's Land, Vash the Stampede, a gunslinger who swore never to take a life, faces his final confrontation with his brother, Millions Knives, who seeks the complete destruction of humanity. As their fates collide, the battle that will determine the future of both mankind and the planet begins.

When Arisu Yamabuki was all alone in bed at night, he was able to find solace in the voice of a radio host who went by "Apollo." However, one day, she simply stopped broadcasting without any explanation. Years then passed, and Arisu is now a second-year high-schooler. He makes it his mission to search for Apollo, as there is something he wants to tell her. He doesn't know what she looks like, or even what her real name is, but he manages to get some leads on her in his school's broadcasting club. That's where he meets four girls who all dream to get a job where they can make full use of their voices! Just who is Apollo, and how will those four's dreams pan out?