[Fate] It's All the Family Tree's Fault!

If Chichibu had a family register passed down for a thousand years; If the current keeper of the family register were a Cú Chulainn fan club president named Bazett; If Bazett manually added a Heroic Spirit section to the family register; If the soul mate field for the Heroic Spirit Cú Chulainn were filled in with Heroic Spirit Emiya, officially and in reality locking them together... what chain reaction would this magical family tree cause? "Yo, Emiya! Caster's old man seems to have done something huge!" the Child of Light said, flipping through the records on the Throne of Heroes. ◆ The pairing is broadly Lancer x Archer: Cu Alter x Black Archer, Cú Chulainn x Shadow Archer, and the original Lancer x Archer. ◇ Related earlier works: ◆ The three main storylines: Cu Alter and Black Archer → Fate/Zero; Cú Chulainn and Shadow Archer → Fate/Apocrypha; Lancer and Archer → Fate/Grand Order. ◇ AU headcanons everywhere. Canon purists, beware.