'No fear' translated one word at a time. The grammar is stilted and the 無し should be kana.

What a Japanese person actually thinks
Reads like a subtitle rendered by someone working too fast. It has the shape of a phrase without being one.

Literally: fear + none
Actually: Comprehensible as 'there is no fear', but the construction is archaic-flavoured in a clumsy way, and writing なし as 無し here is a common non-native tell.

Naturalness●●●●●

Not ungrammatical exactly, but nobody writes this. It reads as constructed.

Coolness●●●●●

The mixed kanji-hiragana-kanji rhythm looks unbalanced as a tattoo, on top of everything else.

medium無し for なし is the kind of over-kanji-fication that immediately marks text as non-native.

不動 fudō
immovable; unshaken

Two characters, dense, and it carries a Buddhist association (Fudō Myōō, the immovable wrathful deity) that gives it real backbone.
恐れ知らず osoreshirazu
one who knows no fear

The natural Japanese phrasing of exactly this idea. Longer, but actually said by actual people.
剛胆 gōtan
bold; dauntless

A real word meaning fearless-in-the-face-of-danger. Compact and strong.

恐れ無し

Orientation: either

N/A — change the words.