On Harvest Moon: Another Wonderful life...?

How do you not have the blue feather? It's given to you automatically by the harvest sprites on Summer 1. Did you check your shelf in the tool shed? To marry Marlin you'll have to go back to Winter 6, have him at 4 red hearts and propose with the feather. I also think you may have to see all of his heart scenes, I don't remember. But yeah, you should definitely have the feather by now.