Mathiason, from what I know, an emperor of minor age who hasn't had his coming of age ceremony yet still isn't technically superseded by a queen mother in terms of hierarchy, but as he is still of minor age many of these political figures such as a queen mother or ministers can dictate policy and orders. This opens up room for a period where the kid emperor is basically a puppet if taken advantage of. The road goes both ways however since while a kid emperor may not have much weight in political decisions, his support is still needed to make the decision seen as legitimate.