Okay, so... The post I saw was either a headcanon, or a small fanfic, I believe it was an ask by someone (can't remember if it was anon or not), and though I don't know who made it, I believe it may have been @altocat, @prismaticpichu, or @holly-sephiroth/@holly-fixation.

I remember that the main characters featured (if not, then the ONLY characters featured) were Zack, Sephiroth, and the garbage himself: Hojo.

I remember that the plot was that Zack was being friends with Sephiroth until one day Professor Hojo injected Zack with a serum that made him not interact with Seph anymore, but then because of the power of ✨FRIENDSHIP✨, the serum's effects stopped working and Hojo's plans were foiled.

I believe I commented on it, something about the Epoch Engage/Operation Noctis AU (Or the "Whatever you want to call this AU because I have no idea what to call it" AU before I came up with the Epoch Engage name as my alternate continuation while Operation Noctis is on Hiatus) and how we avoided that from happening, but I can't remember where the post is.