Once you have completed the marriage requirements, talk to the person you want to marry. You'll both go talk about the proposal at the town plaza. The feather will then be used to confirm the committment between the two of you, and the wedding will be planned to take place in 7 days.
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On the day of your wedding ceremony your fiance will fetch you when you awake in the morning. Everyone will gather in the Chestnut Town plaza to witness the marriage, with Sam overseeing the ceremony. After the short scene you will return to your farm house at 10:00 pm. You won't be able to care for your crops or farm animals, but it will be okay. Your crops won't grow on your wedding day and your animals won't get sick.