恩返し
おんがえし paying back a favour; repayment (of an obligation, kindness, etc.)
Why it means this
恩 (a kindness received) + 返し (repaying) — paying back a debt of gratitude (鶴の恩返し, 'the crane repays a kindness').
Breakdown
Each character links to its full entry — origin story, stroke order, and readings.