Many people have pointed this out before, but I really do think that when it comes to assessing Sua and Ivan’s relationship, taking a look at how her older sister treated her gives good insight into why Sua feels the way she does when it comes to Ivan.
Sua’s older sister was very important to her and maybe the second most impactful person in her life, so when her sister unfairly lashed out and scared Sua, it traumatized her and would go on to affect her future actions and perspective, so given how similar Ivan and her sister are, it's not surprising that his behavior towards her makes Sua uncomfortable.
The way in which Ivan shows intimacy to those he feels a connection with is in the exact same manner as the older sister; they both tease and fuss, which can come across as overbearing and rude, and while this behavior from her sister didn’t seem to initially upset Sua much, after the incident she’s not so fond of it now.
(translations by: sorrowcure & WhataFruit)
That incident with her sister and Ivan’s antagonization of Sua over her plans for Alien Stage are also very similar. They both do so in part because they feel betrayed by her in some way (the older sister because Sua is leaving her and Ivan because Sua’s relationship to Mizi is not the same as his and Till’s), both refer to Sua as being pitiful, and they condescend to her.
It's also mostly because they see themselves in her. While Ivan is relieved to find someone to be “twisted” or selfish like he is, he also despises that part of himself and takes it out on Sua here, and I think the sister is the one here who feels pathetic since she can’t save her little sister who she loves and raised.
While I think the Heavenly Garden comic implies that Sua never got to see her sister again after she was sent to Anakt, her and Ivan’s relationship did have a chance to grow and change but it seemingly never did (as of the content we have so far).
Sua stayed avoidant of Ivan because she didn’t want to be emotionally hurt by him again the same way her sister hurt her (being forced to confront the world in a cruel, uncomforting manner), and Ivan never changed the way in which he showed her intimacy despite knowing it frustrated her (probably because he took her reactions to him as confirmation that his true self was something unlikable, thus believing that he couldn’t improve and staying the way he was with her to try and get any connection he could).
Anyways, look at Ivan hugging Sua
