They mysterious Harvest Goddess lives in the pond next to the hot spring, along the path that leads towards Mother's Hill. She silently watches over Mineral Town and its residents. The villagers can't see her, though they honor her at the Church.
As you have a natural connection to the land, the goddess will make herself visible to you. Throw a gift into the water to see her descend from above to thank you for your generosity. The Harvest Goddess likes gifts of flowers, crops, and edible animal products. She'll accept wool and yarn too, but generally, she does not like inedible gifts like ores, building materials, accessories (Earrings, Dress, etc.), and fished-up junk.
The Harvest Goddess will be appreciative of your gifts and sometimes will reward you for your kindness. The first gift you give to her per day will influence her Friendship Points and Love Points as well as count towards the total number of gifts you give. Tossing multiple gifts into her pond will not speed up her rewards.
10 Total Gifts
After your 10th gift to her, the Harvest Goddess will reward you with a Power Berry. This item will permanently increase your stamina level by 15 points (1 berry icon).
20 Total Gifts
The Harvest Goddess will ask if you have your eye on a special someone. A list of most of the marriage candidates will then appear for you to select. If you don't see the person you like, select the Next Page option to see additional names. You will receive a boost of +3000 LP with the person you choose from this list.
This list is significant if you plan to marry the Harvest Goddess or the mysterious Kappa. One requirement for marrying these special candidates is selecting their name when the Goddess is asking this question. If you do not choose the Goddess or Kappa, then you can never complete that portion of their marriage requirements; they are no longer available candidates for you to woo. Since the Harvest Goddess will only allow you to choose one candidate from her list, this means you can either woo her or Kappa, but not both. If you pick the Harvest Goddess, then Kappa is no longer available to you. If you pick Kappa, then the Goddess is no longer an option. If you choose another candidate, then neither the Harvest Goddess or Kappa can become your spouse.
If you pick Kappa or the Goddess, the Harvest Goddess will reward you with a bag of Relax Tea Leaves. This item doesn't sell through your shipping bin, but it is an ingredient for making Relax Tea. This drink is worth +800 LP with Marie. You'll also receive a bag of Realax Tea Leaves if you are already married when you trigger this scene.
30 Total Gifts
After your 30th gift, the Harvest Goddess will give you a White Grass. This wild-grown item normally grows during Winter, either in the forest south of your farm or in the forest behind the Church. At this point you will receive a piece of White Grass after every 10 gifts.
On a sunny-weather Wednesday since you gave offering #30, you will be greeted by Van the traveling merchant when you exit your farmhouse between 6:00 am and 12:00 pm. Van will stop by to explain that he plans to set up a small shop on the second floor of the Inn on Wednesdays. At his shop, he will sell the Record Player for your house, the accompanying Records, and some tool-upgrade ores (if you didn't want to go into the mine to fetch the ores yourself).
Van will also set up a booth in Rose Plaza on the 15th of every season. This once-per-season store will sell house pets that you can have live on your farm. Van's pet selection will vary based on the season you currently are in.
50 Total Gifts
This time the Harvest Goddess will reward you with an Interesting Book. This item can be found in the bookshelf inside of your farmhouse. Head to your bookshelf, press the A button, and then select the reading books menu. Picking the Interesting Book from the list will fast-forward the game by 1 hour, implying that the book was so engrossing that you lost track of time.
75 Total Gifts
If you liked the Interesting Book, you're bound to love the Really Interesting Book! This book will be added to your bookshelf too. Its story is so enthralling that you'll skip 2 hours of time.
After you have offered at least 75 gifts to the goddess, exit your farmhouse on a sunny-weather Sunday between 6:00 am and 12:00 pm to meet Lou. She has come from Forgotten Valley (i.e., Forget-Me-Not Valley from the Harvest Moon: A Wonderful Life series) in search of cooking ingredients. You can talk to her upstairs at the Inn on Sundays to learn recipes for your kitchen.
100 Total Gifts
The Harvest Goddess will give you her last book, the Super Fascinating Book. Reading this book will use up 3 hours of your precious time.
She will also install an elevator system into the mines. This shortcut will allow you to jump 50 floors at a time, going as far as the last 50th level you've reached. For example, if you have reached floor 68, then the elevator will take you as far as floor 50. For those who reach the bottom 255th floor, the elevator will have stops at floor 50, floor 100, floor 150, floor 200, and floor 225.
150 Total Gifts
The last reward the Harvest Goddess will gift to you is the Seaside Cottage. This new house is at the shore of Mineral Beach, just south of Zack's house. Inside the house, you'll find a table, clock, seasonal calendar, diary, and bed. You can spend the night inside your seaside vacation house, but your family cannot.
In the original GBA game, this house unlocked by linking the Gamecube game and the GBA game together via the GC/GBA Link Cable. Connecting the two games would earn connection stars, with the seaside cottage being the reward for collecting 50 connection stars.