Levels are a core gameplay mechanic in Granblue Fantasy.
Players can level their rank up by accumulating Rank Points (known as RP). Gaining enough RP will increase your rank by 1 and give additional benefits.
The levels of characters can be increased by completing quests, which give Experience (known as EXP).
The levels of weapons, characters and summons can be increased through the Upgrade interface by sacrificing items (also known as foddering). Weapons and characters can be upgraded by weapons. Summons can only be upgraded by other summons. Each weapon and summon has their own individual EXP value when foddered. This EXP value can be increased by matching weapon type as the weapon you wish to upgrade, matching element types or increasing the EXP value of fodder.
The skill level of weapons can be increased by feeding them other weapons with skills. The amount of Skill Rise Rate Points (colloquially known as Skill Points) the weapons have is based on their rarity and skill level.