OKAY, SO, PROBLEM SOLVED
Thanks to your suggestion of using the Log feature (which I didn't know was a thing), I managed to figure out that this was actually a two-layered issue.
The first layer was that my test event had ai = no on it, so it wouldn't actually fire when a character other than the player died at all, because, duh
The second layer was that even without ai = no, it would fire the event in a way that only the AI could see it. What I did was, then, create a second test event, and have the first even scope the second event unto the player
Or to put it more simply, it goes:
on_death = {
events = {
TestEvent.1
}
}
Which triggers TestEvent1, that only the AI can 'see'. But changed it to;
character_event = {
id = TestEvent.1
immediate = {
any_player = {character_event = { id = TestEvent.2 }}
}
}
Now, I'll never see event 1 (even though it totally fires still, I could put stuff in there if I wanted it to be hidden), but event 2 will always show up when a character dies.
The downside is that the event will fire for all players playing, but since my mod is intended for single player only this won't be an issue.