No, it's not really a common theme. Most fanfiction focuses on positive relationships or adventures between characters. But there may be some out - there that explore darker or more complex dynamics.
Deadpool became Deadpool through a series of complex and sometimes convoluted events in the comics. He was originally a mercenary named Wade Wilson, who underwent experimental treatments that gave him his unique powers and personality.
There is a loose link. The version of Deadpool in Wolverine Origins provided a starting point, but the standalone Deadpool movies developed his character and story in a more distinct and expanded way, deviating from the initial portrayal to create a more focused and engaging narrative.
It's a bit of a mixed bag. While there's a link, the portrayal of Deadpool in Wolverine Origins doesn't fully align with his later, more developed storyline. Some elements were changed or not fully explored.
Obviously, the main characters are the two Deadpools. They are both versions of the same character but with potentially different backstories and personalities in this graphic novel.
In a more extreme scenario, Deadpool could end up in Arkham Asylum and think it's a new kind of S.H.I.E.L.D. facility. He'd start interacting with the inmates there, and Batman would have to step in to deal with the chaos Deadpool is causing. Deadpool would see Batman as this dark and brooding figure and keep trying to get him to lighten up.