FictionOnlyReader
I have a couple guesss on why genjutsu. My first guess is he has some bloodline that already exists like Kurama which is good at genjutsu but can have a bad constitution. He’s a part of some new clan or heritage that improves his talent in genjutsu. Then final guess is just general talent in the skill from just latent or from being reincarnated, but I’m leaning towards some bloodline type of thing