I'm assuming Renko in a reverse bunnysuit with Maribel is a meme or gag right now?
Yep. It's the "Renko working at a shady part-time job recommended by a friend" Touhou meme that was created as a result of the reverse bunny girl suit.
Who knows? IIRC, Reiji has PTSD of his own, and that's without previously being driven insane by abyssal influences. I have to imagine the combat medic from that unit would have her own share of PTSD inducing experiences.