It's a normal, stormy night in San Francisco when Uncle wakes Tohru up bc of the "willies". They quickly go to Section 13 and find out that Daolon Wong has returned (with his warriors and the Enforcers) to steal the talismans once again. The original Dark Chi Warriors get trapped within the Urn of Wei Chung and the talisman powers get scattered across the world to the most noble of animals, you get the story.
The Chan Clan had already met Daolon Wong from the filler episodes in Season 2, and Wong already knows about Tohru's secret and sees him as a very useful Dark Chi Warrior. He tries to pursue after him, failing bc Uncle gets in the way everytime. In the episode Ox-Head Incident, with Uncle out of the way in that Orb, Tohru becomes a DCW for a while until Uncle comes in being briefly empowered with the power of the Ox. Then Tohru turns back to normal.
Other than that, I'm not really sure how else differently season 3 would be from canon. Any suggestions/ideas would be nice bc I'm not so good in the AU department. I only know about how to draw them.
For kijker0 , in this AU's Queen of the Shadowkhan, Jackie brings the Demon Archive to the shop where Uncle explains that the Archive contains the spells of the Demon Sorcerors and that they can use it against them. Tohru recognizes this book way back when Shen Du wrote in some spells to take control of the Ninjakhan and is ready to assist Uncle with his research.
Jade is at school being peer pressured to get a tattoo and puts the mark of Tarakudo on her ankle. In that moment, Tohru feels something he hasn't felt in centuries and makes him extra paranoid. Uncle and Jackie wonder what's wrong, but Tohru does not want to jump to conclusions so he waits to see if his gut feeling is true.
And it is. Jackie reveals the the mark of Tarakudo on Jade's ankle when she comes home and when Tohru sees it, he immediately freaks out. When Tohru finally calms down, he explains that the tattoo is the mark of the great Oni King Tarakudo himself, the Lord of all the Shadowkhan, his boss before Shen Du's intervention. He goes on to say when he was serving under Tarakudo, he's seen some humans (and lower level Oni) forcibly branded with that same mark and become mindless Shadowkhan slaves. Before, those memories hadn't bothered Tohru, but seeing Jade with the tattoo does since Shen Du is in control of the Ninjakhan and anything could happen from that. Then the Enforcers with Hakfu attack the shop and like in canon, the ninjas save her.
Before Jade goes to school the next day, Tohru warns Jade to be extra careful, for the mark is very evil and Jade reassures him that nothing will happen. The Enforcers grab the Archive and Tohru and Jackie track down the book to get it back when they see Jade's ninjas giving Hakfu and the Enforcers a helluva spanking. They get Jde out of her dark trance and bring her back to the shop to deal with her.
Jade wants to keep her ninja buddies but Tohru and Jackie will not allow, so Jade pulls the line, "You gave Tohru a chance" to which Tohru replies "But I do not carry Tarakudo's mark". Uncle comes in with the spell to remove the marking when Jade snaps and leaves the shop with the book and kidnaps Tohru to Section 13. Once that's done, she has her ninjas mark him so she can have him in total control as her personal Oni bodyguard, like with Shen Du. She sends Tohru out to bring in ShenMont to translate the Archive.
Jackie does to ninja disguise into S.13 with the potion, gets caught by Tohru and they fight (much to Jade's excitement"). When Tohru defeats Jackie, Jackie is about to be executed and he points out that during their whole fight, Shen Du is running away with the Archive. Jade sees this and sics her ninjas on him just as a disguise Uncle splashes the potion on her ankle, which weakens her hold on the ninjas and Tohru. Throughout the Jade-and-Shen-Du tug-of-war, Jade gets Shen Du to destroy the Archive. Then Tohru's tattoo gets washed off also and is turned back to normal. Still, the power of the Shadowkhan darkness that had compelled him to do such evil things again (even under Jade's control) get him thinking about his olden days in Japan before he traded to Shen Du.