The changing dynamic between Asahina and Suzumiya
It is interesting to compare Suzumiya`s behavior in Disappearance to the one she showcased in the beginning of the series. In Melancholy Suzumiya is presented as a character who uses Mikuru as a tool, and even invited Kyon to harass her.
It also seems that Suzumiya is jealous about Asahina`s looks. When they are conducting the baseball match, Suzumiya ponders about putting Asahina`s hair into a ponytail, but then drops the idea, after looking at Kyon.
However, Suzumiya´s dynamic towards Asahina starts to change into a more positive one, as the series goes forward. A good example of this comes from Disappearance.
Instead of inviting Kyon to take a perverted look at Asahina, Suzumiya is furious at the thought of Kyon trying to take a look at her. She is ready slap him.
Also, around that same scene Suzumiya also displays something else that I find interesting. She says to Asahina that she should be more confidence about herself. While Suzumiya`s approach to it might be a bit of an odd one, she is actually addressing one of the core problems that Asahina has.
Trough the story and especially in her short story, it is revealed that Asahina has a very low self-esteem, and she feels useless since she is not able to do anything. She is not given any useful information from the future. So while Suzumiya´s manner of trying to make Asahina´s feel more confidant might be odd, she is mending in her own way one biggest problems Asahina deals with.
So I think Suzumiya´s relationship towards Asahina has changed to some degree. In the beginning she was only a harasser who saw Asahina as a tool, but I now see Suzumiua acting as this odd big sister figure. She would crush the person who`d dare lay their hands on Asahina. This is quite a big difference to the beginning, where she asked Kyon if he wanted to touch Asahina´s breasts.
Heck, in the second last book, Suzumiya disqualifies those potential club members that were giving Asahina funny looks:
“The guys who started leering at the mention of being able to drink as much of Asahina´s tea as they wanted were obviously disqualified.”
Also, while Asahina still is an mascot character under Suzumiya´s instructions, and she makes her wear outfits that are quite revealing, thus making her a bit of an object, maybe one could see this as Suzumiya´s way of building Asahina´s confidence. Suzumiya sees that Asahina is quite charming, and tries to make Asahina realize and harness this element about herself, by making her wear different outfits.
Also while Suzumiya puts Asahina into such situations, she is quite willing and ready to become an mascot, and enter into that state herself. They both dressed as bunny girls and in the second last book, Suzumiya joins maid Asahina in a flashy china dress.