It's a job title, not a personality trait.

What a Japanese person actually thinks
Slightly funny, honestly. It reads the way 'KNIGHT' would read tattooed on a Japanese tourist in England — the noun is fine, but claiming it is a category error. Nobody will be offended; some people will smile.

Meaning

Literally: one who serves
Actually: A member of the warrior class of feudal Japan. A social position that no longer exists.

Scores

Naturalness●●●●●

Perfectly normal word. The awkwardness is in using it as a self-description, not in the Japanese.

Coolness●●●●●

It's the most obvious possible choice. It signals 'I like Japan' rather than anything about you.

Watch out

mediumReads as claiming a hereditary social class you cannot be a member of. The equivalent isn't 'warrior' — it's 'duke'.

Get this instead

武士道 bushidō
the warrior's code

You can follow a code. You can't be a member of an abolished class. This says the thing you actually mean.
武 bu
martial; the martial way

One dense character covering the whole martial concept, without claiming a title.

On skin

侍

Orientation: either

Brush. If you're doing this anyway, at least let it look hand-made rather than typed.