背中

How it works

The target 背中せなか (back) comes first, then the action. 掻くかく (scratch) shifts to its て (te-form) form 掻いてかいて (scratch), and the bare te-form serves as a casual request — “scratch my back for me.” There’s no polite ください (please) after it, so it’s the kind of thing you’d say to family or a close friend. The object particle を (object) is dropped, as it usually is in relaxed speech.