After his adoptive father Crepus died, and his adoptive brother Diluc found out about his Khaenri'ahn heritage, Kaeya left the Knights of Favonius and moved to Sumeru. During a trip to the desert, Kaeya met a woman named Dehya, who invited him to join the Eremites. The ex-knight was graciously accepted amongst their ranks at 17.

Ever since, he's been one of their mercenaries.