To restore the power of the Sprite Tree, Rowan and the Harvest Goddess want you to make new memories with the villagers of Chestnut Town. They hope that the villagers will remember the old nearby farm to revitalize the sprite's home.
There are several ways to unlock memories: befriending the villagers, triggering various events, and completing activity goals. Once you meet the requirements to unlock a hidden memory, you will see a green alert box appear on your screen with the memory's name. You'll also receive a special reward if you have room in your bag to receive the item. If your bag is full of items when you unlock a memory, the reward will be sent to your house storage instead. If you haven't upgraded your house so that it holds storage, then the reward will disappear forever.
You can give gifts to the villagers for memories relating to their friendship events. These events can trigger once their friendship with you meets or exceeds the music note scale that appears on the dialog box when you talk to the villager. To give a gift, tap on your Bag icon and then select a food, ore, or foraged item (you can't give fences or crop seeds), and then select Hold. Once you're holding an item, tap on the person to give the present. You will see hearts float above the person's head if the person really likes the gift you selected, and you'll earn lots of points towards increasing the person's music note level. A floating music note response will indicate that the person likes the gift, although not as much as a floaty-heart gift. An angry-shaped icon lets you know that the person does not like the gift you gave. You'll still get a little bit of friendship when you give a bad gift.
You have a list of available memories in your main menu. Select the Gear icon to open the main menu, then select the Memories option. Tap on each of the listed memories to learn a hint on how to unlock the memory.
Note: Currently there are two memories in the iOS version that are bugged and still have not been patched. Memory #128 (Worried Citizen) can only be unlocked before you unlock Memory #129 (First Harvest). You can unlock Worried Citizen by lowering your stamina hearts to 1 heart or less, and then talking to a villager; after that you can move forward with unlocking First Harvest. The other memory that is broken is #142 (Flower Master). At the moment the count of the unique flowers you collect will reset for unknown reasons. These two issues means that Memory #150 (An Important Place) will not unlock.