(Technically intestine, but, well.)

鉄心石腸
te-.sshin.seki.chou

Literally: iron – heart – stone – gut

Alternately: Ironclad willpower; unshakeable determination; hardened resolve.

Notes: This is a compound of compounds. Keep in mind that the guts are thought to contain one’s courage and resolve, at least in part; compare phrases like 肝が太い, 肝試し.

This is another invention of our friend Su Shi (蘇軾, Japanese So Shoku). It can be expressed in a bewildering variety of ways, though: the two material elements and the two bodily elements can apparently be switched around at will into almost any configuration as long as the ABAB pattern is preserved.

The creed of this… eight-month-old dude from a video game?