A Critical Hit is a component of combat mechanics that appears in Kingdom Hearts, Kingdom Hearts 358/2 Days, Kingdom Hearts Birth by Sleep, Kingdom Hearts Re:coded, Kingdom Hearts 3D: Dream Drop Distance. and Kingdom Hearts Union χ.
A Critical Hit can randomly occur at the end of a weapon combo at a rate determined by the Critical Rate, and will increase the damage dealt by the combo finisher by a set amount known as the Critical Bonus, as well as potentially launching or stunning the target. In most of these games, the Critical Rate and Bonus are hidden stats for each weapon and attack, vaguely indicated by their descriptions, although in 358/2 Days these stats are given explicitly. In Re:coded, however, the Critical Rate does not vary between weapons or attacks. The Critical Bonus is generally additive, as in Kingdom Hearts, Kingdom Hearts Birth by Sleep[?], and Re:coded[?], but is multiplicative in 358/2 Days and Dream Drop Distance. The Critical Rate and Bonus can also be further modified through abilities like Critical Plus and All Critical, or accessories like the Sight Unit Ⓛ, Critical Ring, and Critical Sun.
In Kingdom Hearts, a Critical Hit may also occur at the end of attack combos that are part of special abilities; for Ars Arcanum, both the seventh and thirteenth hits are considered combo finishers able to become Critical Hits. Slapshot also has a chance of dealing a Critical Hit, while Counterattack is always considered Critical. Certain enemies also have unique reactions to being dealt a Critical Hit. For example, a Critical Hit will cause the Black Fungus to drop a rare Mystery Mold, and will prevent the Sheltering Zone from splitting into a school of Sea Neons upon its death.
In Kingdom Hearts, each Keyblade will generate a different sound when dealing a Critical Hit. In 358/2 Days[?], Birth by Sleep[?], and Dream Drop Distance[?], there are no audio effects beyond those normally associated with a combo finisher, while in Re:coded, a Critical Hit has a more pronounced sound than a finisher, and generates a small shower of sparks around the Keyblade.