That notebook with the FMA drawings in the beginning was Hitagi's, she is kind of an otaku herself, she's especially a big fan of FMA. If you take a closer look she's the character to make the most references regarding anime/manga pop culture, even if the anime cuts some of those bits.
2021-10-16 07:32:55 +0000 UTC
The rest of the series timeline jumps quite a bit, so if you feel like an important event happened offscreen, you’ll learn what happened eventually.