person always at one's side; constant companion
Refers to someone who is always nearby, like a shadow, often implying a close, inseparable relationship. Can be used for a loyal friend, assistant, or even a persistent follower.
He is always by her side like a shadow.
Those two are like constant companions; they go everywhere together.
Compound of 影 (kage, 'shadow') and 身 (mi, 'body, person'), literally 'shadow person'. The exact historical derivation is uncertain, but the word evokes the image of a shadow that never leaves one's side.