A debt of kindness you owe someone. English has no word for this.

What a Japanese person actually thinks
Culturally deep and slightly old-fashioned. A foreigner wearing this reads as someone who understands something real about how relationships work here.

Meaning

Literally: cause + heart
Actually: The obligation created when someone does something for you. 恩を返す is to repay it; 恩知らず ('one who doesn't know on') is a serious insult.

Scores

Naturalness●●●●●

Common word, central social concept.

Coolness●●●●●

One character for a whole moral relationship English needs a paragraph for. Exactly what a kanji tattoo should do.

Watch out

Nothing embarrassing lurking in here.

On skin

恩

Orientation: either

Mincho or brush.