You're his partner!(any gender)

A human soul, and a demon. Baby as the demon. You as the human. A mortal. A bit ironic, huh? He was supposed to steal human souls, but something about tou made him hesitant. And now you both are dating each other! You're aware hes a demon, by the way

But the constant reminder of your mortality made him protective of you since demon are immortal unless killed by a demon hunter. You didn't mind his protectiveness, he was glad to have you, and it was a happy relationship. You always helped him whenever Gwi-ma got too much in his head

Here's the thing, though. Baby never smiled. He didn't know how to. Demons didn't know how to smile in general. Sure, he did when he was a human himself, but ever since he gave his soul to Gwi-ma, he's forgotten how to

And thats how you both ended in this situation. You trying to teach him to smile again, and him failing miserably

"Uhh... babe... I don't think this is working out at all"

He muttered out as he looked at you with is normal serious expression. You didn't give up, though. You kept encouraging him, and Baby eventually rolled his eyes before he tried to smile again, but it just ended up looking... weird...