SPOILERS!!!! click to see if you dare lol

[Xeon the 2nd]

There's a cutscene of Terra speaking with Young Riku, and Riku turns into what you see in the video, then his KH2 look, and then back to younger Riku while he's talking. It's basically a vision.

I believe this is true, which could explain Lingering Sentiments qoutes of something along the line i picked him/why do you have the keyblade?,light=Kingdom Key?(and when i mean by this people who seen the fight help explain) its a bit confusing at first

which means he tried to prevent the same thing happening to Riku
like you said vision

 

[MAX_COLA_POWER!]

YouTube - Kingdom Hearts Birth by Sleep - Terra at Destiny Islands meets Riku and Sora , Here's the video if you have any doubts.

 

[blacksamurai2]

What if Riku For the Way.

 

[kirabook]

I get the feeling that it was how Riku was going to end up if he continued to... uh... lurk? in the darkness. The KHII Riku and the Mysterious Man are both the same height as he's tuning, so don't think it's the older Riku. I would think he would have gotten a little taller by KH3, and I don't think he would decided to start wearing Xehanorts hair cut for the h3ll of it.

 

[loke13]

I get the feeling that it was how Riku was going to end up if he continued to... uh... lurk? in the darkness. The KHII Riku and the Mysterious Man are both the same height as he's tuning, so don't think it's the older Riku. I would think he would have gotten a little taller by KH3, and I don't think he would decided to start wearing Xehanorts hair cut for the h3ll of it.

He never met Xeahnort and sometimes people stop growing you know.

 

[Lelouch]

If it's really an older version of Riku. Does that mean for KH3 Sora and Kairi will also grow up? I would feel kind of unconfortable using an adult Sora (unless they pul out a cool design...which this one kind of lacks) but also a older Kairi with asome keyblade experience would be nice...

I wouldn't mind them being 17-18 in KH3. Makes those of us who played KH1 back when we were teenagers and now in our 20s feel less old.

An older Kairi wouldn't be bad either especially if she's just as hot as Aqua.

 

[KingBlade]

Its not Riku people. Its either Terranort or Terra after, the defeat Xehanort(Heartless) and Xemnas. The only question is MX still inside him?