Since a lot of people seem to like Jonny Ariga a lot, why not write a fanfiction about him? If you do, may I make a suggestion? Here's what I think would happen:
After Vincent and Katherine got married, Jonny continues his search for his soulmate. Along the way, he meets Catherine and accidentally fallows her to the Underworld. And now Jonny and Catherine must work together to stand up to Catherine's father. And also, Jonny and Catherine start to grow closer to each other.