Here's how it works:
✔️ If your relationship with Rin is between 0-20, she will like Fruit Ice.
✔️ Once it reaches 21-40, she will prefer Donuts instead.
✔️ At 41-60, a Plant is a great choice.
✔️ At 61-80, she'll love Ice Cream.
✔️ And if you've reached 81-100, she'll appreciate a Nice Plant the most!
The same applies to Nao:
✔️ 0-20: Fruit Ice
✔️ 21-40: Plush
✔️ 41-60: Plant
✔️ 61-80: Beer
✔️ 81-100: Nice Plant