Pro Hero Katsuki who finds out about his "number one fan" who insists on having every piece of merch. Once he meets Izuku for the first time he decides he wants him. Izuku is actually more interested in the merch than the man so Katsuki +

decides to offer to give him the first of any new merch of his directly to Izuku in return for a sexual favor. Izuku is more than happy to oblige just so he can brag about his new merch while refusing to give away who his "sugar daddy" is.

Alternate Romance Flavor: Izuku gets the merch in return for one date and through this process Izuku falls in love with Katsuki.
Added Hilarity Flavoring: Katsuki takes Izuku on so many dates Izuku ends up married to Katsuki but still upholding his end of the bargain