I think Momo should have a new ability, Skill card fusion, which allows him to combine 3 different equally ranked skill cards to form a random new one of a higher rank. if all 3 are of the same weapon type then the random fused card will be of the same weapon type. if all 3 cards are the same, then the fused card will be a higher rank of the same card.
As is, my inventory is just piling up with skill cards that I'll never use, I think this could make for a great means of clearing the clutter as well as a ryou sink.