YOU OUTSIDE MY WINDOW

A blurb if this were on something like MyAnimeList:

Byleth Eisner of 2-B (not to be confused with Byleth Eisner of 2-C) is just your normal, everyday student in Garreg Mach High School. But one day, the mysterious Yuri Leclerc from 2-A approaches him and asks him to help Yuri from other students who are trying to hurt him! They may be strangers, and Yuri may be kind of weird, but Byleth never turns down someone in need. Still, just why are people after Yuri? And will Byleth and Yuri get along better than they both thought?

In the style of a 12-episode slice-of-life high-school anime, this 100k fic is all about our two main characters going on little misadventures in their school. While the main focus is obviously on Byleth and Yuri, other characters feature prominently (F!Byleth, Edelgard, Dimitri, and Claude) and pretty much every 3H student is mentioned throughout the work.

You can find Chapters 1 to 4 here on AO3, and previews for Chapters 5 to 12 in the screenshots. File comes in both PDF and EPUB format (although EPUB unfortunately has a few formatting errors, like no page breaks).