noun
backscratcher
A long-handled tool for scratching one's own back. The name literally means 'grandchild's hand', from the idea that a grandchild's hand is ideal for scratching an unreachable itch.
See also: 麻姑
孫の手で背中をかく。
I scratch my back with a backscratcher.
From 麻姑の手 (Mako no te), referring to the long fingernails of the immortal Mako in Chinese legend, which were said to be ideal for scratching an itch. The kanji 孫 (grandchild) is a later reinterpretation.