Yes, the untapped power that lies within you. Now, child, it's time you awakened that power and realized your full potential.
Prime - Maleficent 6★ Medal
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The Leviathan (リヴァイアサン Rivaiasan?) is a form of Roxas's Kingdom Key which appears in Kingdom Hearts 358/2 Days. It can be upgraded to the Leviathan+. This Keyblade can be a great weapon for combos, as all of its abilities add to combos.

Stats

Kingdom Hearts 358/2 Days
Leviathan
Stats
Strength Magic
Base Unit Ultima Base Unit
+0 +0 +0 +0 +0
Defense Crit Rate Crit Bonus
Base Unit Base Unit Base Unit
+0 +0 +6 +0 +2 +0
Attack Speed Approach Speed
Ground Air
1.0 1.0 1.0
Obtained
Attach Elegant Gear 4
Kingdom Hearts 358/2 Days
Leviathan+
Stats
Strength Magic
Base Unit Ultima Base Unit
+0 +0 +0 +0 +0
Defense Crit Rate Crit Bonus
Base Unit Base Unit Base Unit
+0 +0 +6 +0 +2 +0
Attack Speed Approach Speed
Ground Air
1.0 1.0 1.0
Obtained
Attach Elegant Gear +4

(Note that all weapons' abilities are obtained by equipping 1 or more Ability Unit(s) to their respective weapon panels)

Trivia

File:Windmaker.jpg
Pre-release screenshot of 358/2 Days showing the Keyblade's Wind Maker form

.

During 358/2 Days' development, the Keyblade was to take an aerial attack-oriented form known as the "Wind Maker" when the Wing Gear was equipped. Both the Keyblade and Gear were ultimately cut and the Wind Maker's appearance given to Leviathan.