Simple, warm and correct.

What a Japanese person actually thinks
Clean and unpretentious. The single character has a faintly classical air that 友達 doesn't, which works in a tattoo's favour.

Meaning

Literally: friend
Actually: Friend. Slightly literary alone — the everyday word is 友達.

Scores

Naturalness●●●●●

Correct; the bare 友 is a touch formal but entirely natural in writing.

Coolness●●●●●

Four strokes, good diagonal movement, ages well.

Watch out

Nothing embarrassing lurking in here.

On skin

友

Orientation: either

Brush.