This has probably been mentioned elsewhere but the Eizouken OP has one of my favorite small, understated details in the character splashes and what the borders imply about the character.
Asakusa’s border is a tilted jumble of vaguely rectangle-ish shapes that loosely line up to form a jagged frame. It looks like someone hastily covered the screen with a bunch of post-it notes, which is something you could absolutely see someone with a scattershot attention like Asakusa doing.
Mizusaki’s a bit tidier, with a clearly defined rectangular border appropriate for someone who has to at least keep up appearances, but it’s still unaligned enough to tell that there’s an underlying looseness that makes her more similar to Asakusa than she might appear at first glance.
What the rigidly straight lines in Kanamori’s border imply, then, is really obvious in contrast to Asakusa and Mizusaki, but it is worth noting that it’s not a perfect grid - there’s still some minor disorder in the varying rectangle dimensions, which tracks with how Kanamori isn’t cold and clinical to an inflexible and unempathetic degree, she would just really prefer if things were planned and dealt with in an orderly manner.