#fumey

They came to mind as a crackship, but the more I thought, the more parallels I saw.

Both are older sisters

Both are focused on achieving something for their younger sibling (Goku Fubukihime wants to un-snowman-ify her brother, Fumey wants to avenge her sister's death)

Both have deep mental unwellness (Goku Fubukihime went mad and presumably became criminal in pursuit of fixing her brother, Fumey stewed in her hatred for yokai and let it fester towards herself for hundreds of years in the name of revenge)

As for how a pairing like this would even happen, it's as simple as Fumey deciding to get that bread by going after the Goku yokai, starting with Goku Fubukihime. She fails to catch her, and Goku Fubukihime fails to freeze her, leading to a cat-and-mouse game that has these two clashing and getting closer.

Fumey and her sister grew up in a soulcery clan that believed all yokai are evil

Her sister was very sympathetic to yokai, while she didn't really care about them

One day, the Azure Dragon broke out of his soul gem and destroyed the clan

The last thing Fumey saw before she died was her sister's soul get taken away by the Azure Dragon, and when she woke up, she'd become a Smogmella yokai

Naturally, given her upbringing and the situation, Fumey was very very upset, and it took a while to come to terms with anything. Eventually she does, and she swears vengeance and a hatred for all yokai (herself included now)

To get stronger and put food on the table, Fumey became a yokai bounty hunter (mainly in the human world). She's rather ruthless in her work, as a yokai hater.

Her use of smoke to obscure her work and the glow of her hair has earned her the title "The Red Haze"