On crafting the Backpack Blueprint, you need the 1 x Mastela Fruit to craft this bag pack. The only way to obtain this item is from a certain kid named Mitt, Admin of Official Events somewhere in Prontera, where you were offered a Mastela Fruit for exchanging a number of items.
This NPC can be found on the center part of the map in Prontera, just besides Kafra Staff. Find a kid that wears a teddy bear headgear, he has a speech bubble that says Cute Boy from….
Talk to this kid and he will asked you to exchange Mastela Fruit for the following items:
- 5 x Seed of Mastela
- 1 x Honey
- 10,000 Zeny
Seed of Mastela and Honey can be acquired from the Pet Labor or Pet Adventure. You can also buy Seed Mastela from the Exchange for 29,189 Zeny and the Honey for 2,653 Zeny. (This price will change from time to time.)
Once you have those items, you can now exchange it for Mastela Fruit.
Now, you finally have the Mastela Fruit for crafting the backpack.