Same problem as 母 — it's the formal reference term, not the affectionate one.

What a Japanese person actually thinks
Formal and a little distant, which is a strange note for a memorial or tribute tattoo.

Literally: father
Actually: Father, in the humble form used when speaking about your own father to others. Direct address is お父さん.

Naturalness●●●●●

Correct word, register mismatch.

Coolness●●●●●

Four strokes, clean shape, no warmth.

恩 on
the debt of kindness owed

Says what a parent actually gave you, in one character.

父

Orientation: either

Brush.