Well, definitely R.I.P godjacob Fufufu, with godjacob out of the way I'll be able to take over Konoha! kukuku!
But, all things considered, only Main Oc's would get lengthy backstories. I'll need to kill off Minato though, and like...every other named character. Too pacifist.
Azumi, Kenji, Tomiko...I'd say those are the characters who'd sorta require a back story to have the same depth as other Main Ocs. This'll be a good opportunity to plunge the world into Chaos! I'll need to hurry and work out the kinks in Sagiso's new Hiden -Tempest, or maybe Hurricane Release?The name still needs some work.
Hmmm, strictly speaking, it won't be a terribly large amount of work to do. The first order of business will be to betray and subjugate Sunagakure. Then we'll slip their poison into the streams of the land of waterfalls and annihilate Takigakure.
On the topic of Mori, well, backstories don't need to be tragic. I don't particularly consider Furijia's to be a pity story, since I just want to use it to flesh out her ideology and turn her into a character who's mostly nice but understands when to be ruthless. Ruthless enough to unite the ninja forces within the land of Fire and then march on Kusagakure, kukuku.
You can make a casual type of backstory, like first mission or something like that. My first ever attempt at Rping was writting out an assassination~ Well, lemme not give Shen any ideas on how to assassinate the Daimyo, I'll leave out the evil monolgue on this one.
Or do something like his Academy days and how he came to admire Tomiko. Your rock kingdom will be a kingdom of dust after I'm through with it though, so don't put in too much effort. kekek~
You and godjacob can make the world all Fuwafuwa Before I dye it red with the crimson of anarchy! I wonder if I can devise a plague-release? Disease is usually a good way to sow chaos.
Or even where he got his scar from, it should be quite the story. So too will the bards sing of the dark ages when the fire nation- I mean, the Land of Fire attacked!