Karma — but specifically the version where the bad thing comes back to you.

What a Japanese person actually thinks
Slightly ominous. When someone says 因果応報 it's usually while watching a villain get what's coming. It reads less like 'I believe in balance' and more like 'you'll get yours'.

Meaning

Literally: cause + effect + response + retribution
Actually: Buddhist cause and effect: your actions produce consequences that return to you. In practice Japanese uses it almost entirely about *deserved punishment*.

Scores

Naturalness●●●●●

Common, well-known idiom.

Coolness●●●●●

Four dense characters and genuine Buddhist grounding. The punitive slant is the only thing to weigh.

Watch out

mediumThe positive 'good karma' reading barely exists in Japanese usage. This phrase mostly means retribution.

Get this instead

自業自得 jigō jitoku
you brought it on yourself

If the punitive sense IS what you want, this is the blunter, more common version.
縁 en
the karmic thread connecting people

If you wanted karma as connection rather than as consequence, this is the warm half of the idea.

On skin

因果応報

Orientation: vertical

Mincho, vertical.