This is for the one commenter who wanted a little more sadistic so I thought of the most sadistic headcanons for you, ok maybe no too sadistic like the rhaast headcanons I have yet to post but it's soft and sadistic enough, enjoy~!
🌸The blissful and courteous facade that he puts on seems to be such a wonderful act for truly ignorant spirits. Perhaps if you stay long enough he can truly be himself around you.
🌸Once his true side is revealed maybe it was best for you to listen to those "misinterpretations" about him, though if you are this far gone with him there's no escaping his grasps now.
🌸The father you thought him to be was truly an executioner, or maybe torturer of souls would fit him. The whole time you were wrapped up in his crazed demon fantasy, what Thresh saw as saving and blossoming potential was torturing souls till he saw fit.
🌸Maybe you could help him see his wrongful ways? Oh but honey he knows what he's doing.
🌸Since the two of you would be dating his dark obsession would wrap around you, the choice of whether you submit to it or not is up to if you could live with a demon doing those things to a spirit that could've been you in another lifetime
🌸"My dear do you really think I care about these souls? I mean they are flawed but I like to witness them relish in their mistakes and transgressions, makes it even much more delightful"
🌸Since you've come this far in dating him expect him to grow an obsession with you if you are living, I mean he can't really hurt the living, but don't worry love he wouldn't dare even lay a finger on you
🌸The obsession only worsens once you pass into the spirit realm once your mortal life ends, because now he can be with you for eternity
🌸Don't worry he'll still be the sweet soft Thresh you met who'd take you on dates and flirt with you but expect the teasing to be amped up
🌸All In all Wholesome Sadistic Soft Boy 🌸