You have to buy them from the shop that you give salmon to Aki , I think it just spawns randomly unless you use the Sushi Pudding item which will spawn one in I believe. At the shop on the right side there's a candy machine which will give you a random price and candy
Dude, I got it from the vending machine, and I managed to give it to my sister, but the strange thing was that she got a purple heart, which unlocked several new actions, I thought it was cool
The red heart is Favor, the purple one is Desire, and if Desire high enough, you'll something cool to playing with her xD (The purple one just appear if you had the red one first).
