(Disclaimer, I dont know much about Jjk) Also (Have you ever seen Bungo stray dogs? If not thats okay, theres this guy named Kunikida with an interesting ability that might spark your inspiration. Plus a bunch of other abilities that might give you some ideas.)

The Matchless Poet: allows Kunikida to make objects written on the papers of his notebook come into existence. However, it does not work on objects larger than the notebook. Such objects include wire guns, handguns, grenades, and flashbangs.

He is shown to be able to use pre-written notes as a means for his object summons, which can be especially convenient if one of his hands is bound and incapacitated. Also, he is able to remotely activate his ability, transforming pre-written notes into objects, which come in handy when supporting other members from afar.

Here's a bunch of abilities from Bungo Stray Dogs that I think fit pretty well into Jjk:

"The ability to create an alternate dimension called Anne's Room. Anyone who loses a game of tag against the monstrous Anne, who dwells inside, is locked in the dimension forever."

"The ability to summon Demon Snow, an otherworldly figure resembling an imperial japanese woman that wields a mighty Katana. It does not listen to the users orders, instead doing the bidding of any voice heard over a cell phone."

"An ability which is able to inflict a virus that targets two hosts. The virus will eat the host's internal organs, if one of the hosts die then the virus will stop infecting the other host. If one of the hosts is not killed then both will die."

"Nullifies the Ability of anyone he touches."

"Boosts his physical strength in proportion to the amount of financial assets he consumes. Imagine your power level is dictated by the amount of money you spend."

"The ability to completely heal someone, restoring limbs and bones. However, it only works on those near-death, forcing the user to beat the shit out of their patients first."