So in my Sora and Vanitas swap AU, Sora takes the role of Vanitas being all of Ventus's “Darkness” Everything is the in this but just that Sora still has his hero-happy personality with a pinch of Vanitas personality too you know. And, since everything is likely the same as normal bbs universe that means Sora has the same relationship that Vanitas has with his Master, Xehanort. (If you read the novel you would know what I mean idk if you did ) And, with that Sora tries to make Xehanort proud and happy for him. (He just wants a loving father-and-son relationship but knowing Xehanort he not gonna have that.) Which starts his envy of Ventus having stuff he doesn't.

At the beginning of birth by sleep before Aqua and Terra starts their exam Xehanort tells Sora about the Keyblade X and how if he wants Sora to merge with Ventus so he can have it and that he would be proud of him if he could do that for him. Which, Sora of course is happy because “He would be proud of me!” But, Xehanort knowing how excited he would get by this news, Xehanort tells him the downside about it which is if he doesn't do it he’ll kill him, Sora is Struck by this but doesn't give up on himself.

All that stuff in the game blah, blah. Just that Sora is thinking about being whole again. Being whole means he and Ventus would be together but he doesn't know if he wanted that. He kinda like being his own person and felt happy just being Sora. This whole situation makes him go down a spiral with his emotions getting worst making the monsters he created stronger.

But, he doing this for his Master and he needs to make him proud of him. On the battlefield, Sora feels nervous and scared and tells his Master I don’t about doing this also that he wants to be his own person Xehanort doesn't take it kindly to this new and tells him to do it or else... Which, Sora tire to act bravely while he completely crumbles under the scenes.

And, yeah, yeah, all that stuff happens and Sora and Ventus make it into Stations, and before Sora tells Ventus that he is finally proud to do this and his master would be proud of him too. But Ventus is like “What if I destroy the keyblade?” Sora didn't think bout that part, “I don’t know. But all I know is that I’m winning this…” Ventus chuckled “Hm, alright then. We’ll see…” They fight yeah, yeah. And before fully finishing off Sora, he tells him that “The keyblade is the both of us So if I destroy it I’ll destroy you as well.” This Throws Sora off his game and sends him into a fit yelling and screaming at Ventus, “You get everything! Everything that I wanted! A loving family, friends, and praise! Hell, you even get to be your own person!” As those words fell out his mouth Ventus give him the final strike.

Ventus smile and laugh n laugh before noticing, he was crying and shaking. “Sora...?” “This is all your fault! Do you think I wanted to do this?” Ventus watched as his other half was in pain and he feel every bit of it...“I hate this job...Every out of I had just ended up with me dying...” “I don’t understand. Then why did you do it?” “I just wanted someone to be proud of me...That's all...” Before Ventus could get a word in Sora faded away leaving him all alone with feel horrible feelings and regret…

(I gotta get back to this story lol)

I read the lauriam story file and also cry also, are you still interested in the Sora swap Vanitas story you ask about? (I have the story explained already in my notes)