Strength Boost

Power Boost is an item that raises your strength by one point. In Kingdom Hearts, this item is called Power Up instead. Like the AP Boost, it can only be used from the stock menu once obtained. They can be found in treasure chests and through made through item synthesis.

In Kingdom Hearts Final Mix: Beginner Mode, Sora starts off with 8 Power Ups in his stock.

Kingdom Hearts

 * Traverse Town - Mystical House, Yellow Trinity.
 * You can receive another Power Up by mailing the 10th Postcard.
 * Olympus Coliseum - Complete the Hercules Cup in under three minutes.
 * Deep Jungle - Complete the Shadow Cavern course of Jungle Slider.
 * Agrabah - Storage Room, activate Green Trinity.
 * Halloween Town - Guillotine Square, ledge near the Lab Entrance.
 * Neverland - Clock Tower, return when the 2:00 and 4:00 doors are lit.
 * 100 Acre Wood - Tigger's Giant Pot, rare nut reward from Owl.
 * Hollow Bastion - Entrance Hall, on ledge near Lift Stop exit.
 * End of the World - Gate to the World x2

Kingdom Hearts II

 * Olympus Coliseum, in the Underworld Entrance.
 * Hollow Bastion, Cavern of Remembrance: Mineshaft
 * Defeating Xemnas in Garden of Assemblage.

Kingdom Hearts
In addition, they can be synthesized from List IV by using the following:


 * 5 Power Shards
 * 3 Power Gems
 * 1 Power Crystal
 * 1 Mystery Goo
 * 2 Orichalcum

Kingdom Hearts Final Mix

 * 5 Spirit Shard
 * 3 Spirit Gem
 * 5 Power Shard
 * 3 Power Gem
 * 1 Dark Matter

Kingdom Hearts II
Besides synthesizing them, they are rewarded for completing certain Moogle List:


 * Obtain 35 Synthesis Material types
 * Obtain all Energy-type Materials.

To synthesize a Power Boost, you need the Guard Recipe and these materials:


 * Mythril Crystal x 1
 * Blazing Crystal x 3
 * Lightning Crystal x 3
 * Lucid Crystal x 3
 * Serenity Crystal x 1

Trivia

 * Sora's max strength in Kingdom Hearts II is 153. This can be raised to 166 with items and Fenrir, and to 172 by using a Drive Form.
 * Increasing Sora's strength increases the damage of Goofy's limits and Genie's Valor limit.