如鱼得水 (rú yú dé shuǐ)
During the Three Kingdoms (sān guó 三国) , Liu Bei (liú bèi 刘备) went to Longzhong (lóng zhōng 隆中) three times to ask Zhuge Liang (zhū gě liàng 诸葛亮) to assist him. Finally, Zhuge Liang helped Liu Bei deal with military and politics affairs, and was significantly trusted by Liu Bei. Their respect for each other became deeper. Liu Bei said to his ministers: “Having Kong Ming (kǒng míng 孔明) help me, I feel just like a fish which has been put back in the water.” This idiom is used to signify finding a boon companion (愉快的伙伴) or an ideal situation.