This is the story of an Archer-class Rama traveling through various worlds at Gaia's behest.
Planned story arcs:
Strike the Blood - Campione! - The Myth of Hades arc / Witch on the Holy Night (interwoven) - Fate/Zero - Tsukihime - The Burning of Fuyuki arc - The Garden of Sinners - The Great North American Mythological War - Black Bullet arc / Divine Realm of the Round Table: The Last Savior (interwoven) - High School DxD / Absolute Demonic Front: The First Steel War God (interwoven) - Final Singularity: The Grand Time Temple - Tales of a Thousand Years Past, the Birth of the Last King - FGO Part 1.5, Chapter 4: The Witch Trial - The End of Everything and a New Beginning.