I would say Vivi, but because she'd try to flirt and end up yapping about her favorite things like stars and cheese or something.

She's a silly goblin.

Deimos would unintentionally be good at it. But he says something earnestly and its like damn i believe him

Riley is a flirt and very good at it, but he reserves it for those that interest him.

Amber is a big oni woman with thighs that can crush melons and boulders. She is also kinda awkward about it depending on the person. Flirt to mess with someone, easy. To someone (Deimos) that she genuinely likes, she'll blurt something out or suggest they fight. Very physical love language.