The name Iron Spirit in Chinese / Japanese...

不屈 is the short form of a longer Chinese word and also a word used in Korean and Japanese to express the idea of being indomitable. It literally means “will not bend,” “will not crouch,” “will not yield,” “will not flinch,” or “will not submit.”

Note: Some will translate this as “indomitable spirit”; however, technically, there is no character to suggest the idea of “spirit” in this word.

See Also:  Tenacity | Fortitude | Strength | Undaunted

不屈不撓 means “Indomitable” or “Unyielding.”

不屈不撓 is a long word by Chinese standards. At least, it is often translated as a single word into English. It's actually a proverb in Chinese.

If you want to break it down, you can see that the first and third characters are the same. Both mean “not” (they work as a suffix to make a negative or opposite meaning to whatever character follows).

The second character means “bendable.”

The last means “scratched” or “bothered.”

So this really means “Won't be bent, can't be bothered.” I have also seen it written as “Will not crouch, will not submit.” This comes from the fact that the second character can mean “to crouch” and the last can mean “to submit” (as in “to give in” such as “submitting to the rule of someone else”). This may explain better why these four characters mean “indomitable.”

Notes:
Some will translate this as “indomitable spirit”; however, technically, there is no character to suggest the idea of “spirit” in this word.
Other translations include indefatigability, indomitableness, or unremitting tenacity.

The first two characters can be stand-alone words in Chinese.
In Japanese, this is considered two words (with very similar meanings). It's more common to see the word order flipped to 不撓不屈 in Japanese.
The same characters are used in old Korean Hanja. Just like in Japanese, the words are swapped to 不撓不屈 creating a word pronounced “불요불굴” in Korean.

See 不撓不屈

See Also:  Tenacity | Fortitude | Strength | Undaunted

負けじ魂 is a Japanese proverb that means “indomitable spirit” or “unyielding spirit.”

Note: Because this selection contains some special Japanese Hiragana characters, it should be written by a Japanese calligrapher.

百折不屈 is a Korean proverb that means “indomitable spirit,” at least, that is the way it is commonly translated in martial arts circles (Taekwondo, Hapkido, etc.).

The literal translation is “[one] hundred [times] broken [still] don't succumb.”
Or more naturally translated, “Even if attacked/beaten one hundred times, still be undaunted/indomitable.”

Notes:
Some will say this is one long word rather than a proverb.
This is also a proverb/word in Chinese though rarely used in modern times.