What's the backstory behind Dark Signer Leo?
Ohoho, so u know the Sawyer Fight?
Basically, the finishing blow did too much damage to Leo. Bro hit his head too hard and when Luna was escorted out and Sawyer was going to drag him out to a room to rest, he realizes that Leo isn't exactly alive anymore. Not expecting this, Sawyer panics a bit and hid him into a more secretive floor, while lying to Akiza that he just may need alot more rest than they thought. (I like to think this secret room is also where Misty's brother was killed cause we love the parallels)
Leo on the other hand, is met with the Earthbound Immortal Siwi Mach'ac. He was heavily against becoming a Dark Signer until Siwi Mach'ac made it into a deal. Which is, the Earthbound Immortal will break Ancient Fairy Dragon from her prison and make sure she is able to get back to Luna, in exchange for another level 7 synchro.
There's also the added bonus that Leo almost have free reign to do whatever. Like, Siwi won't care if Leo goes to tell Yusei about the plans cause it's entertaining. But I say almost because of course, Siwi would not let Leo forfeit or do something that can endanger himself. Cause u know. Dark Signer linked to the Earthbound Immortals an all. No, u will not throw both our lives away.
So, that's how it starts! Leo makes a deal and tries to give his pals the upper hand as much as he could while also trying to strategize a suicide deck without Siwi Mach'ac being aware.