Kiritsugu never lost his family, never became the magus killer. A First Generation Magus by the name of Shawn David Lacich takes Kiritsugu's place, simply taking out scum bags and monsters, no dream of being a hero, no emotionless. The Grail is not Corrupted. When Iri becomes the Lesser Grail, Shawn decides to break his contract in favour of wishing for her back. its works and Irisviel becomes pregnant, however, the Einzbern find them, Kill Shawn, and Take Irisviel, modifying the unborn child to be a Humunculi lesser grail. the child would be born, named Sean Patrick Lacich. when Sean turned 14, he ran away, taking his mother with him. 3 years later, the fifth holy grail war starts. Sean decides to summon the Lancer class(Elizabeth Bathory), his mother summons a servant as well, Saber, reuniting with Artoria.
Sean is able to force Miracles to happen, so need be, if he dies, he can make Elizabeth independent of a master, not needing one. By the End of the war, the only Servents remaining are Elizabeth, Tamamo, and Saber. Elizabeth being supported by one last miracle granted by Sean, to allow her to act independently, her wish, for them to see each other again. Her wish would allow Sean to Appear in Chaldea, but also cause the heroic spirits of that war to remember him as well.

fifth holy grail war

Saber(Artoria)
master Irisviel

Lancer(Elizabeth Bathory)
Master Sean

Archer(EMIYA)
Master Rin

Rider(Medusa)
Sakura(she was rescued by Sean and Irisviel after they learned what was happening to her)

Assassin(Jack The Ripper)
former master unknown, current master Sean(forced a miracle to allow himself to support two servants easily)

Caster(Tamamo No Mae)
Master unknown (supported by unknown means???)

Berserker(Kiyohime)
master, Ryuko himeji(Sean's Stalker)