im sure im not the first person to point this out, but i find it so interesting how miki and kozue are basically identical save for the slightest difference in hair, both style and color. kozueās hair is darker than mikiās, which as far as color coding goes is pretty straightforward: the āpure,ā naive sibling and the cynical, jaded siblingālight and dark. but then thereās also the matter of kozueās upwards swoop in the back of her hair, as opposed to mikiās which is kept neatly, straight down his head.
at first, you could easily just assume that itās a matter of kozueās hair being slightly longer than mikiās, but then akio accelerates his car in āmikiās nest box,ā and the back of mikiās hair flies up, and suddenly resembles kozueās. kozueās perpetually windswept ādo is suddenly contextualized as symbolic of her knowledge of sex (as a tool for power), which miki only truly becomes aware of in akioās car.
but to do so, mikiās bangs also fly up, losing his previous point of commonality with kozue. right before akio speeds up his car, miki is āgivenā the wheel (figuratively speaking). for miki to gain the hidden knowledge of adults (back of his head, obscured from view) that kozue possesses, he must also lose all common ground with her (front of the head, identical head on). he must shed his childish fringe that evokes his innocence and his sameness with his sister (one and the same, see: the sunlit garden), which is further complicated by the fact that they are both more and less similar than miki thinks.
ultimately, mikiās sexual maturity requires him to distinguish himself from kozue (visually thru gender performance but also thru power, ie, where to sit in the car), since leaving childhood means becoming a man means exerting power over brides and princesses and witches (which both his objects of affection/obsession, kozue and anthy, illustrate are not in fact discrete designations but rather just slightly different labels applied to the same thing, only dependent on how youāre looking at it/her).
as a girl, kozue has the āfreedomā to be interpreted in many different ways and embody many different roles and possesses many different ways of understanding herself and others within the patriarchal system of ohtori (by embodying multiple ontologically meaningless labels at once). she can, at least superficially, āchooseā how to navigate her own exploitation. miki does not even have the illusion of choice. the path he must take has been chosen for him: he can either be a prince or a failure.