minor thing: sua wasn't able to become an idol for a variety of different reasons (physical capacity, skill, drive, etc), but one of them i never see discussed is that she is fundamentally not made for idol life - the reason she dies first in alnst is also commentary on this. it's her mental fragility that has more implications for her character.
being an idol necessarily consists of the performance of a desired image to the audience. mizi is individually suited to this (unknown, her image shifts to suit the viewer's desire of her as extension of the lack of consideration for her interiority), but sua demonstrates an unwillingness to perform this happy idol image outside her relationship with mizi. and even when she does act through this idealised romance, unlike mizi, who lives within the fantasy, she is unable to immerse herself in it, only being able to obtain joy vicariously through mizi. (the image above: only mizi has light in her eyes - becoming an idol is initially her dream to claim a fraction of independence for herself.)
sua positions herself as secondary and supplemental to mizi, like a manager & her star in the spotlight. from this role she finds her purpose. she supports mizi, corrects what is unbefitting of an idol, and expects dependency for her labour of responsibility. sua is dependent on mizi for meaning and emotion, while mizi is dependent on her for more physical comforts (shelter, support). sua can't live without mizi, but mizi can eventually live without her if she wished to. this is why sua is so desperate for mizi, and to ensure an eternity together at any cost.
refusing independence due to her self deprecation, sua enmeshes herself with mizi. she traps herself in their union - she has nothing outside of it, and so naturally takes the sacrifice against existential threat for the two of them when it comes to it, if she can help it. this is what dictates her direction for both r1 in zomst and alnst, and this dependence on mizi for identity is what stops her from succeeding idolhood.
