I found it funny that Sua with her low mental strength is the one trying to shield Mizi, who has high mental strength, but then I realized that it made a lot of sense.
Sua was trying to protect Mizi the very same way she had wanted to be protected with her low mental fortitude.
This is further corroborated by the fact that her biggest trauma stemmed from her sister instilling in her her own fear of Sua's death by describing the horrific practices of Anakt Garden in excruciating detail.
It makes sense that Sua would then take the opposite approach and try to protect Mizi by keeping her from the same words, actions, and knowledge that had traumatized her in the past.
In a way this too is a sacrifice. It means Sua gives up having someone to confide in and seek companionship from when exposed to the various horrors their world still has to offer.
By being determined to keep Mizi in the dark, Sua is also throwing away the comfort and protection Mizi would want to give in the moments when she's scared and afraid.
The morning probably won't come to me
Like a lie, if all this is just a dream
(You hug me tight as if nothing happened)
It's just sweet dream, it's today
Wait for me, I'll go see you soon, ooh
Lord, please when the song is over,
— Sweet Dream, reflecting Sua's feelings going into Round 1
Yet no matter the form, self-sacrifice is inherently an act of selfishness and Alnst backs up this message again and again.
It is the whole one-sided aspect of self-sacrifice that makes it selfish.
Despite it involving multiple people, only one person is required when making that decision — themselves. And by deciding on their own, they're effectively rejecting communication and discussion, thereby showing no respect for the other person's will.
What can be more selfish than overriding someone else's feelings for the sake of your own?
Self-sacrifice doesn't need the other party's consent.
It doesn't ask for their opinion.
It doesn't give them the right to choose, because the choice is already made for them.
In the end, it's one decision made independently by an individual on behalf of someone else, and that someone else will be the one to shoulder the results.
