Kaeya Alberich is the adopted son of the Ragnvindra clan, a famous wine magnate in Mondstadt.

It has been a long time since he last called Diluc Ragnvindra "brother".

Keya currently serves as a cavalry captain in the Ordo Favonius and is a trusted lieutenant of the real Master Djinn.

If there is trouble in Mondstadt or its appeal, Kaeya is often the only one who can deal with it. If you are looking for Kaeya, you are unlikely to find him at the Ordo Favonius headquarters.