What if Kaeya was a decade younger than Diluc?
Crepus still dies on Diluc's 18th birthday, a knight is holding back baby Kaeya as he screams for the family he only just got
Afterwards, Diluc holds him close and promises he'll never let him go because in the span of a few months or maybe a couple of years Kaeya has lost two fathers and nearly lost two entire families
But Kaeya still has that overwhelming guilt swelling up in his chest and he breaks down sobbing and crying to Diluc about how sorry he is and how he didnt mean too.
Diluc gets angry, murderous angry, but not at Kaeya. How could this adorable, sweet child possibly be to blame? And no, he's not angry at Khaenri'ah and Kaeya's (deceased?) Family, by this child's description of his home, leaving him anywhere but that hellscape was clearly the better choice.
So who is he so mad at? Well, he digs through his father's office and finds a hell of a lot of information linking the fatui to Khaenri'ah and the delusion that killed his dad.
So now Diluc is getting revenge for his dad and baby brother starting with killing a hell of a lot of Fatui agents. He doesn't know what the root cause of all the peril is in this world, but he plans on finding out.
The Dark knight hero has his peacock
(Alt: Batman has his robin)
