The Blue Feather is a recurring item in the Harvest Moon series. It acts as a sort of engagement ring. In Harvest Moon: Friends of Mineral Town, it is used to propose to the bachelorette that you wish to marry. The Blue Feather's function is exactly the same in the girl version of the game Harvest Moon: More Friends of Mineral Town to propose to the bachelor that you wish to marry. It's an item that is required for marriage.