I would give grayfia 10 phenex tear and let Issei used it. Then charge the 10 phenex tear on his account again. 10 times of half death should let him remember for a while. And then shrink his D to nothing. Maybe even shrink his organ so he got a slow death.
Its all for Issei man.. Like the world literally revolve around him so of course as long as you're enemies,your status is not matter. He could even poop in your shoes and you have to wear it like nothing in it due to his protagonist halo..