Unlock Mystery Events:
Raise your seeds and then harvest their fruit and you will receive Special fruit items from the Field Guardian which you can use to unlock secret events.

Unlock Mystery Field Events:
The first three intervals are unlocked by giving the man a Sky Blue Seed and Mystery Soil, Crimson Seed and Blossom Branch and Silver Seed and Whale Tail.

Unlock New Game Bonus:
Successfully complete the game and then 'Save' when prompted. Start a new game and play up to the point of Kaede's Village and find the cat there and you will be able to retain ALL your characters techs from the previous game along with some Exp.