how is roxas connected with com

roxas is there cause he's needed,after Naminé mess up with Sora's memories,Xion and Roxas need to be in someplace that Naminé can put their memories in Sora,that's why he's on a Virtual Twilight Town,if u play the 358/2 you'll understand

 

Xion is quite literally SPOILERSPOILERSPOILERSPOILERS: a manefestation of Sora's memories that he lost when he went to sleep at the end of CoM. END SPOILERSPOILERSPOILERSPOILERSPOILERS

 

I'm warning people now, this post is going to be spoilerific, and to make things easier on myself, I'm just gonna go post everything I can think of, even if somebody already has. So, if you don't want to learn some things that happened in the games (Namely 358/2 Days), don't read my post.

The reason why Roxas exists after Sora was restored from being a heartless is that Roxas (Being Sora's nobody) is Sora's body. This is something you'd only know from playing the Final Mix versions, but from Sora being a heartless all the way to joining up with Roxas, Sora didn't have a body. Instead he was just a free-floating heart that gave the appearance of his body, exactly like Xehanort's heartless (Again, something you'd learn from the Final Mix games. If you wanna know more about this part specifically, go ask the member Starkiller).

Roxas looks like Ventus because at the end of Birth By Sleep, Ventus's heart goes into Sora. Which means, among other things, that Sora has had at least three hearts inside of him. When he became a heartless, Kairi's heart went back to her and Ventus's heart most likely went to Roxas, making Roxas the only nobody with a heart.

Admittedly, Roxas doesn't play much into the overall plot of Chain of Memories. Instead, he is hinted at and became foreshadowing. When Sora went into the memory of Twilight Town, Vexen said that it was a memory from the other side of his heart, i.e. Roxas. To be perfectly honest, Roxas does nothing for the plot in Chain of Memories aside from that. Roxas had nothing to do with Sora being put to sleep at the end of Chain of Memories. That was done so Namine could fix his memories, because she screwed with them so badly it was basically a train wreck.

Now, Xion. First off, she is not a nobody. Xion is a puppet created by Vexen (Similar to the Replica Riku). Xion was created to ensure the Organization had a keyblade wielder that was loyal to them in case Roxas wasn't. Xion would fulfill that purpose by absorbing Sora's memories, preventing Namine from fixing them and Sora waking up. She was supposed to eventually absorb Roxas, forever preventing Sora from waking up. When that time came, Roxas defeated Xion and basically absorbed her instead. This allowed Namine to continue with fixing Sora's memories and this is also why Roxas is able to dual wield keyblades. Roxas, pissed off at the Organization being the ultimate cause of him killing Xion, went to The World That Never Was in order to destroy them. Riku (On orders from DiZ to capture Roxas), got in the way and stopped Roxas. They put Roxas's body in the fake Twilight Town to keep him safe until Sora was ready to absorb Roxas again and become whole.

In relation to 358/2 Day's title, the day Roxas goes to attack the Organization (And looses to Riku in the process) is the 358th day of Roxas's existence. KH2 starts on the 359th day of Roxas's existence. The seventh day for Roxas in KH2 is the 365th day of Roxas's existence, or basically a year after he was created.

Did I miss any important details?

 

Confusing, but it makes some sort of sense