It's the object. Two strokes that say 'knife'.

What a Japanese person actually thinks
Reads as a noun on a label. Two strokes gives it almost no visual presence, and it names a thing rather than saying anything.

Meaning

Literally: blade
Actually: A single-edged blade — a sword, but also just a kitchen knife in compounds (包丁 is a different character, but 刀 is the generic blade).

Scores

Naturalness●●●●●

Correct word.

Coolness●●●●●

Two strokes. As a tattoo it's a shape, not a statement.

Watch out

lowExtremely low stroke count means it reads as a mark rather than a character at small sizes.

Get this instead

武 bu
the martial

The concept rather than the object. Far denser and it actually says something.
剣豪 kengō
a master swordsman

If you want the swordsman rather than the sword. Two strong characters.

On skin

刀

Orientation: either

Bold brush — it needs every bit of weight it can get.