Hux develops a new kink for feeding and trying to fatten up Kylo which Kylo enjoys way more than he could've expected. To their mutual delight, Kylo's usual intense training routine doesn't lead to him losing this new weight, merely converting a lot of it to muscle mass albeit with a thick layer of fat on top.

Hux can't keep his hands off this new meatier Kylo.

Bonus for comparisons with Hux's own skinny twig-man body.

Slight preference for top!Kylo (with dom!Hux) but Hux banging Kylo like a greyhound mounting a bullmastiff is good too.