魚心あれば水心あり（うおごころあればみずごころあり）

Japanese vocabulary

Meaning: kindness begets kindness; you scratch my back and I'll scratch yours; if a fish is kind to the water, the water will be kind to the fish

See it used in real works

• Example sentences from Japanese novels & web fiction (Massif)
• Hear “魚心あれば水心あり” pronounced in real videos (YouGlish)