The only master and apprentice in the Afterlife Department are Yi Bing and Huo Ling, respectively. Though, they know that these two would soon later turn to be a husband and wife. Just look at the change in Yi Bing. Not only did Yi Bing's personality mellowed, but he also now started to care more about his fellow grim reapers, as well as the Afterlife Department unlike before that he ignores them and only when something important happens in the Afterlife Department would he help.
After all, Gu Shi is the head of the Afterlife Department. Yi Bing has already given the position of the director of the Afterlife Department to Gu Shi. It is not as if they would think that Yi Bing regretted his decision of giving the position to Gu Shi, or that Yi Bing is intentionally showing Gu Shi his (GS) incompetence. But that this is Gu Shi's job. If Yi Bing wanted to help, then it is good. But if it is too much help, then it would not look good.
