So there seems to be a thing here that when there’s Saigenos involved, Mumen is usually Saitama’s wingman and Fubuki is usually Genos’s wingman(wingwoman, you get the idea).
What if they’re at a bookshop trying to find romance advice books and they see each other, finding that they’re both helping a hero out. Trade information, and they find out they’re helping one side of a relationship.