Fudoshin (Japanese: 不動心) is a state of equanimity or imperturbability (literally and metaphorically "immovable heart" or "immovable mind") - a philosophical/mental dimension to a (commonly Japanese) martial art which contributes to the effectiveness of the advanced practitioner.

Fudoshin: A spirit of unshakable calm and determination, courage without recklessness, rooted stability in both mental and physical realms. Like a willow tree, powerful roots deep in the ground and a soft yielding resistance against the winds that blow through it.

Fudo Myo is a Buddhist guardian deity (and patron of martial arts) who carries a sword in one hand (to cut through delusions and ignorance), and a rope in the other (to bind 'evil forces', and violent or uncontrolled passions and emotions). Despite a fearsome appearance, his aspects of benevolence and servitude to living beings are symbolized by a hairstyle associated with the servant class.