You know, Soul Eater Not! makes a lot more sense and becomes a lot more tolerable if you think of it as a self-insert fanfic written by Tsugumi instead of actual canon spin off material.
I mean like, just think about it. Tsugumi is a big fan of Soul Eater, so she writes a fanfic where she is a new student at DWMA (a VERY common trope in Soul Eater fanfics). She’s Japanese, so it explains why her knowledge of American history and America in general is off.
Tsugumi isn’t a good fanfic writer, so all of the Soul Eater characters end up being OOC (e.g. Spirit perving over under age girls, the kids not acting as obnoxious as they should be since they’re like 12). Everyone instantly likes Tsugumi or if they don’t like her right away they will soon enough.
Can’t have a good fanfic without some OCs, so Tsugumi comes up with Anya, Meme, and the others. She doesn’t really have any idea how to make them interesting or well-rounded, so she just makes them extremely exaggerated anime cliched character archetypes and wing it from there (Anya is the tsundere ojou and Meme is the big breasted ditz times infinity). Again, both Anya and Meme instantly like her and want to become her meister for some vague, unknown reason.
As for Akane, he could easily be someone Tsugumi has a crush on in real life, so she inserted him into the fanfic so he could be sweet and flirt with her. However, since Tsugumi doesn’t really know Akane, Akane in the story kinds of end up like a glorified Marty Stu. Bonus! He’s a distant relative to one of the canon characters! Double bonus! Said canon character isn’t supposed to have any living relatives!!!