I understand that this is off topic, but...
OH MY GOD. Now that scene in Re:coded finally makes sense! How did I not figure that out by now?
XD It was done in a purposefully vague way, but once you connect the dots it makes sense. SoD was the one gathering the people who would be potential Darknesses from throughout time in his bodyless form, the time the island was destroyed was when Riku was his most vulnerable to the Darkness, the Riku we meet in Prankster's Paradise (Monstro) is his "dark side".
KH3D said:
Riku: That was my...my dark side. I gave in to the darkness once. And ever since, it's chased me around in one form or another. The Seeker of Darkness who stole my body...a puppet replica of the shadows in my heart...and now, I'm facing me.
The memories in Re:coded that were of Riku weren't originally a part of the Journal, but rather memories that were implanted in the Journal by Naminé.
Re:coded said:
Jiminy: Gee, now that can't be right. If the data was repaired, we should be seeing the things that were written inside my journal, right? But what we just saw--that never happened. Or, at least, I never wrote it down.
Donald: You mean it's showing us stuff you don't know about?
This could be interpreted as if the memories in the Journal are from regular ol' Riku from the time when the islands were destroyed where he first meets SoD, but Riku by that point had already left via the portal and
had arrived in Hollow Bastion, looking for Kairi and Sora because he thought they would have been with him when he made it off of the world. This isn't the behavior of somebody who was
walking through a destroyed world and willingly walked through a portal made by a stranger with full knowledge he was alone.
There was no way that scene in Re:coded could have logically happened in the timeline we know exists, and yet there it is.
But Naminé herself provides the answer:
Re:coded said:
Naminé: It all began with these memories that were sleeping way down deep in Sora's heart.
Sora: These are my memories?
Naminé: No. Not yours. These belong to people connected to you.
Tada~ These were Riku's memories, but he probably doesn't remember them (because of time travel hijinks and stuff.)
(I had a long rant about the memories and how they got into Sora's heart to begin with for Naminé to show them in the journal but I think it is better for a theory because we have no concrete proof of it yet)