Level Up is an option in the Collection tab of the Spirits mode. It allows players to level up primary spirits in order to increase their stats or enhance them into stronger spirits if possible. There will be a list of spirits which can be sorted into various categories, any spirits that are at max level and can't be enhanced will be blurred out. Once players select a spirit to level up, they can choose to level up spirits using snacks or cores.
Snacks (おやつ, Snack) are solely used for levelling up spirits, giving them experience. However, this process also costs SP, meaning it must be done with a bit of caution. The player may hold a maximum of 999 of each type of snack.
Ways to collect Snacks
A green snack, the smallest of the snacks. Gives 250 experience and costs 8 SP. These are also the most common.
An orange snack, medium sized. Gives 1000 experience and costs 32 SP. While not as rare as a large snack, they aren't as common as a small either.
A red snack, the largest of the snacks. Gives 5000 experience and costs 160 SP. However, these are the most rare.
Cores are mainly used in summoning spirits, but can be used as an alternative to snacks. Cores can only be obtained by dismissing spirits, granting SP based on the spirit's class and number of slots it uses (for support spirits only) and a core of that spirit's type and class. Once obtained they can be sold, used in summoning, or be fed to spirits to level them up. Up to 99 of a spirit's core can be obtained; any extra cores gained while at 99 of that core will be lost.
As a snack
Just like snacks, cores will give a spirit experience at the cost of some SP. Feeding a spirit a core that has a matching type to that spirit will give it 30% more experience at no extra cost.