One major aspect of gameplay in Harvest Town is the ability to form relationships with characters, including the villagers, and the bachelors and bachelorettes that you can one day marry (currently marriage is not yet available). Creating relationships and increasing fondness with characters will allow you to progress in the game, gain rewards, unlock events, learn more about the citizens, unlock relationship rewards, and even receive the occasional gift from them in the mail.
To check your relationship progress with each villager, go to your BAG and select SOCIAL tab. It will display the list of villagers and their relationship progress (the number of hearts) they have with you.
In order to become friends and even romantic partners with the citizens of Harvest Town, you will need to increase your fondness. Fondness is increased by giving gifts the characters like, by talking to them, and by completing quests they give you from the bulletin board, in the mail, or in person. You can have a maximum of 7 hearts with regular citizens and 12 hearts with bachelors and bachelorettes. Once you have reached maximum hearts with a citizen, a message will pop up saying “___ likes you very much!” when giving them gifts. After maxiumum hearts are reached, you no longer need to give them gifts.
When receiving a relationship reward from a citizen, it may sometimes take a few days for the gift to arrive. Be sure also that you are at the correct amount of hearts by giving them an extra gift as the journal does not always display hearts properly.
You are able to give as many gifts as you want, with up to 100 Fondness per week. When you try to gift a character whose limit has been reached, they will reply something along the lines of, "[Name] doesn't seem interested." Weekly fondness is seen on the NPCs profile page under the social tab and resets every Monday. On birthdays, gifts are worth x2 more than they usually are, and are part extra fondness rather than the weekly fondness.
Citizens react differently depending on the present, which results in different levels of fondness. There are 4 classes of gifts: favorite, liked, neutral, and disliked. Each NPC has a favorite item as well as a category of items that they like, as indicated on their profile. Their favorite item will result in the most fondness. Fondness received from gifts is also affected by the gift's quality, so higher quality gifts will give slighter more fondness.
See NPC Gifts Table for a quick overview of all gifts.
Disliked levels are not confirmed.
Specific NPCs are romanceable, which you can see under the social tab labeled as “single.” These citizens have a maximum of 12 hearts can be married after reaching 10 hearts with them. It's not certain at this point if same-sex marriages are allowed.
To marry an NPC you have to first reach 10 hearts with them. After that you have to purchase 7 x Flower bouquet (each costs 50 gems) from the Fishing Shop. After gifting your bachelor 7 x Flower bouquet you have to gift them a wedding ring which you can buy at the Fishing Shop for 1500 gems or gain it from the Wishing Tree. To complete the wedding you will need the full wedding suit which you can also purchase from the Fishing Shop for 999 gems. So all together you will need about 1349 or 2849 gems and 10 hearts with that NPC to marry them.