Level

Level is a numerical representation of a character's battle experience. In the Kingdom Hearts series, a character accrues Experience Points when enemies are defeated (regardless of if they are in the active party), and when enough Experience has been gained, the character "Levels Up." Each game rewards leveling up differently.

The maximum level in Kingdom Hearts and Kingdom Hearts 358/2 Days is 100, whereas in Kingdom Hearts: Chain of Memories, Kingdom Hearts II, and Kingdom Hearts Birth by Sleep the maximum level is 99.

Leveling up
Upon gaining a Level Up, a character is granted a boost to one of their attributes, and sometimes coupled with a new Ability or equipment expansion. Listed below are all the rewards you can get for each individual game. This includes level up rewards for not just Sora, but also for Donald and Goofy, except where noted.

Kingdom Hearts

 * 1) Increase in Hit Points.
 * 2) Increase in Magic Points.
 * 3) Increase in Strength.
 * 4) Increase in Defense.
 * 5) Increase in Ability Points
 * 6) Gain a new Ability.
 * 7) Increase in Accessory slots.
 * 8) Increase in Item slots.

Kingdom Hearts: Chain of Memories
In Kingdom Hearts: Chain of Memories, the player is presented with three choices upon leveling up. The choices available depend on whether that option has been selected in the past and whether Sora or Riku are being played.

Sora
Sora can increase his HP, Card Points to allow him to create bigger decks, or every three levels, he can learn a new Sleight for use in battle. If a Sleight is not chosen upon the current Level Up, it will stay available as a choice for each new Level until it is selected.
 * 1) Increase in HP.
 * 2) Increase in Card Points.
 * 3) Learn a new Sleight.

Riku
Riku can increase his HP, his attack power to deal more damage, or increase his Dark Points, allowing him to stay in his exclusive Dark Mode for a longer period of time.
 * 1) Increase in HP.
 * 2) Increase in Attack Points.
 * 3) Increase in DP (Darkness Points).

Kingdom Hearts II
In Kingdom Hearts II the only way to gain HP, MP, and certain abilities is to complete scripted battles and earn the "Get Bonus", which hugely differs from the other games in the series.
 * 1) Increase in Strength.
 * 2) Increase in Defense.
 * 3) Increase in Magic. (Only Sora and Donald)
 * 4) Increase in Ability Points.
 * 5) Gain a new Ability.

Kingdom Hearts 358/2 Days
In Kingdom Hearts 358/2 Days, although a level is gained each time enough Experience is amassed, the character does not actually increase in level at that point. Instead, they receive a Level Up panel, which increases the character's level when installed into a panel slot or by itself. There are also link panels that double, triple and quadruple the levels gained from the LV Up panels linked to them.

Kingdom Hearts Birth by Sleep
In Kingdom Hearts Birth by Sleep as with the other games leveling up leads to stat boosts, though most stat boosts are gained from accomplishing in-game objectives.
 * 1) Increase in Strength.
 * 2) Increase in Defense.
 * 3) Increase in Magic.

Bonus Level
The Bonus Level is a reward system exclusive to Kingdom Hearts II and Kingdom Hearts Birth by Sleep, because no experience is gained from bosses. Sora, Donald, Goofy and (if applicable) a fourth party member will receive a Bonus Level after each boss fight in Kingdom Hearts II, receiving a "Get Bonus," and in Kingdom Hearts Birth by Sleep, Terra, Aqua, and Ven as well. The original Kingdom Hearts didn't have this particular system, instead just giving the player certain rewards upon completing scripted events.

Kingdom Hearts

 * 1) A new spell or upgrade to an existing one (for Sora and Donald).
 * 2) A new Ability.
 * 3) A new Accessory.

Kingdom Hearts II

 * 1) Increase in Hit Points.
 * 2) Increase in Magic Points.
 * 3) More Armor slots.
 * 4) More Accessory slots.
 * 5) More Item slots.
 * 6) A new spell or upgrade to an existing one.
 * 7) An extra Drive Gauge. (Only Sora)

Kingdom Hearts Birth by Sleep

 * 1) Increase in Hit Points.
 * 2) Extra slot for Deck Commands
 * 3) A new Command Style

Form Level
Every Drive Form (except for Anti Form) can be upgraded as well, which can only be Leveled Up by gaining a separate form of Experience, which is only accumulated under certain circumstances while in that specific Form. As a Form levels up, it acquires another Form gauge (allowing Sora to stay in the Form longer), and its Growth ability will also be upgraded. Sora will also receive Abilities to use outside of a given Form as well, like MP Haste learned from Wisdom, and the Growth ability of a corresponding Form (at Form Level 3 you gain the ability, and at 5 and 7 it Levels Up). Forms can have Growth abilities up to the Max Level (7), while Sora can only have the ability up to level 3.

Kingdom Hearts
There is no way to level up your summons in Kingdom Hearts, but you can increase the amount of time they stay on the field by equipping the Cheer ability to Sora, Donald, and Goofy.

Kingdom Hearts II
In Kingdom Hearts II, Summons can be leveled up by using any one of them. You earn one point of summon experience for every Summon Gauge that is consumed while a Summon is on the field. Once enough points are gained the Summon Gauge increases so any Summon can stay out longer.