Many people have fond memories of meeting a certain teenage boy in their younger years. However, their ages vary widely, and each remembers him as a teen. This story follows the intricate intertwining of their various stories and how this young man, who apparently lives outside of time, has affected each of them.

The Blue World, which symbolizes reason, is under constant attack by the creatures called the Nightfly O'Note originating from the Red World, symbolizing instinct. Akira Asagi, the 17-year-old protagonist who is a researcher at Blue World, is nominated to lead the war at Ryuukyuu LAG, a proud defense facility on the islands of Ishigaki and Iriomote. She meets the sixth combat unit "IS," which was formed four years after a fierce battle that annihilated the fifth unit. Akari must lead these six riders, also called the Scared Rider Xechs, to fight against the other world while at the same time deepening the relationship among them.

Shidou Itsuka faces greater peril than ever due to his continued involvement with Ratatoskr. He has already sealed 10 Spirits, and Isaac Westcott, leader of Deus Ex Machina Industries, has finally decided to kill Shidou and plunder the Spirits' powers for himself. To achieve his goal, Isaac declares an all-out war against Ratatoskr, forcing the organization to exhaust its resources to ensure Shidou's survival. Despite being severely outnumbered and outmatched, a glimmer of hope exists in the form of the Spirit of Time, Kurumi Tokisaki. Shidou must seal and acquire Kurumi's power to travel to the past and confront the Spirit of Origin—the catalyst that started it all.

An unseen evil lurks in the streets of Paris. Unless something is done, the darkness will unleash its destruction and consume all that is good. The City of Love will be lost to her people forever. All hope rests within the hearts of five young ladies. The only problem is, they don't even know it yet. But will an apprenticed nun, a reserved aristocrat, a hardened criminal, a traveling circus emcee and a Japanese girl experiencing loss set aside their unique differences and come together as one for the defense of many. The Paris Fighting Troup is born.