Why are there Bear characters and how do I remove them entirely?

[Meneth]

The events can affect AI

No it can't, unless you play with Unrestricted Supernatural Events; default is that supernatural events can only happen when a player is involved.
If you play with Unrestricted, then all bets are off; you'll have Demon Children all over the place, Glitterhoof in every Lunatic court, Werewolves, and so on.


The chance of it happening is 1 in 10 000 per year BTW. Unless you've got Unrestricted on, you'll see bears roughly once every 20 full campaigns; a lot more rarely if you only play for a few centuries each campaign like most people.
For comparison, the "Hole to Hell" event happens 12 times as often.

 

[Meneth]

is there some game file I can delete or move to a flash drive so I can literally set it on fire?

Open bear_events.txt.
Add "always = no" to the trigger of the first event there.

Or just disable Supernatural events.

 

[Meneth]

I am half-tempted to add a "This is unbearable" option to the last event in the bear chain that undoes the bear transformation.