one of my favorite ven & vani au ideas is where like. after some of the KHUX stuff comes to light and they find out that vanitas isn’t just half of ven’s soul, but also a “reincarnation” of the original darkness that inhabited ven’s body, like. ventus figures “okay what if he acts on demon rules. what if i had ‘sold my soul’ to him back then and now it’s like, his”. and instead of freaking out he’s like ‘how can i use this to my advantage’ and figures “if i sell my soul to someone else will vanitas try to defend his ‘property’” and it actually ends up working. ursula? dealt with. dr facilier? gone. bill cipher? extend your hand for a handshake and ventus’ attack dog is on you. ventus is using his own soul as leverage and vanitas is just “this is MINE no one else TOUCH IT” and everyone is waiting for this to blow up in ven’s face but somehow it doesn’t. ventus just keeps trying to sell his soul and vanitas keeps coming out of the shadows to rain hell down on anyone who tries to make a deal with ventus.