『Fanfic』Kamen Rider Geats x Honkai: Star Rail: An Interstellar Rider!

The Herta Space Station is seen being attacked by intergalactic monsters from the Antimatter Legion, followers of the Path of Destruction. Amidst the chaos, two Stellaron Hunters, Kafka and Silver Wolf, infiltrate the station and steal the Stellaron that was being safely held within it. Kafka takes hold of the Stellaron and inserts it into the body of an empty vessel generated by Silver Wolf. The vessel known as Stelle awakens, after which Kafka erases her memory, informs her of the future that lies ahead, and leaves. Stelle then fall unconscious.

A now-amnesic Stelle wakes up and meets March 7th and Dan Heng. Both are traveling on the Astral Express, a large cosmic train that travels the universe along the eponymous "Star Rail". After eliminating the remaining threats from the Antimatter Legion, Stelle meets Himeko, the Navigator of the Astral Express, and Welt Yang, an interstellar traveler originating from the world of Honkai Impact 3rd. In an attempt to discover their origins and eliminate the threats of the remaining Stellarons, Stelle departs with the Astral Express crew.

... Or that's what "Destiny's Slave" Elio wrote in his script. However, beyond Elio's expectations, the Remembrance Aeon, Fuli, summoned Ace Kaslana - Kamen Rider Geats, who is another interstellar traveler originating from the world of Honkai Impact 3rd, to Herta Space Station and departs with the Astral Express crew. And from there, a future that "Destiny's Slave" could not predict began.