expression
kindness begets kindness; you scratch my back and I'll scratch yours
Proverb meaning that if you show goodwill to others, they will respond in kind. Literally: 'if a fish is kind to the water, the water will be kind to the fish.'
See also: 魚心あれば水心
魚心あれば水心ありというから、まずは自分から親切にしてみよう。
They say kindness begets kindness, so let's try being kind first.