In Harvest Moon, you must use a Blue Feather to propose to the girl that you would like to marry.
There are 5 elligible wives: Ann, Ellen, Eve, Maria, and Nina. Once you reach heart level 5 (you can see their heart level in each of the girl's diaries) and you have upgraded your house, you can buy the Blue Feather from the Peddler for 5000 G.
After using the Blue Feather to propose, it will disappear if the girl you proposed to accepts.
- The use of blue feathers to propose stems from the symbolic Bluebird of Happiness, representing, nonetheless, happiness, auspiciousness and prosperity of many sorts. Its use as a symbol of marriage and love stems from the tale of The Blue Bird from French fairy tales.