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. Often used to describe reciprocal relationships. The literal meaning is 'if the water has a mind for the fish, the fish will have a mind for the water'.
See also: 魚心あれば水心
水心あれば魚心で、彼が親切にしてくれたから私も手伝った。
Kindness begets kindness: since he was kind to me, I helped him in return.
ビジネスでは水心あれば魚心の精神が大切だ。
In business, the spirit of mutual give-and-take is important.
A Japanese proverb of uncertain origin, likely derived from the observation that fish thrive in clean, kind water and in turn enrich the water. The exact historical derivation is uncertain.