Fanfic ideas help

Hi everyone, lately I've been writing a fic with the intention of diving deeper into the psychics of the Saiki K world. The one leading the investigations is Kusuo's younger sister, who doesn't have powers of her own but can interfere with the powers of others. The problem I have is that I can't figure out creative origin stories that would explain why characters have psychic powers. With the Saiki family I intended to have it explained by the ghost of Saiki's dead paternal gandfather, but no clue as to what he could explain. With toritsuka I obviously wanted to connect it to the fact his father was a monk, but there's no info available about the mother so I don't know how that would play out. I really need ideas so anything can help! If you're interested you can ask me anything, I have a lot of other details thought out that I won't rant about rn.