So I happened to look back on some of the early chapters, and I noticed something: it seems a lot of the pages in between chapters features one of the characters (both mains and minors) and some representation of their iris (Tooru being the obvious exception). One thing I found pretty noteworthy about this is that the end of chapter 8 features Katagiri. Now, for those who don't recall, she was the girl from Hijiri's flashback who had a crush on him and had an iris that could predict danger. Anyway, the reason I say this is noteworthy is because, despite the function of her iris being clearly stated in the story, we never saw how exactly her iris was represented. The between chapter page I mentioned, however, portrays her holding a road sign which depicts a time and date (as well as a symbol which very much relates to how her iris was used in the story). One could make the assumption that this is what Katagiri sees with her iris.
With that said, I noticed that Fujimura, the teacher with an iris, was another character whose iris never actually appeared in the series, even though the function was alluded to (albeit just speculated instead of directly stated). I tried looking to see if, like Katagiri, the visual representation of her iris would appear in the between-chapters pages as well, but it seems that a few of the chapters are missing those at the end. Whether they were left out by the scanlators, or if they were absent even in the actual tankoubon, I'm not sure, but now I'm interested. If there are any missing pages like that, would anyone here be able to post them?