Hello Alright so I am new at this. Before I start I haven't played BBS I've only watched some play throughs and cutscenes (I don't own a psp).

 

What I've been thinking is there is a scene where MX tells Ven "To find is to lose and to lose is to find" the same line, coincidentally that Marluxia used on Sora in COM. after making that parallel I decided to replay COM and while playing Riku's story I remembered the second option Namine gave Riku. He could either stay awake and confront and eventually control the darkness in him or he could go to sleep and she could lock his heart and make it so Ansem SOD doesn't escape. Taking that into consideration, I was thinking maybe they could get Namine to seal the darkness in Terra.

 

That's just an idea I had. What do you guys think?

terra doesnt need to have his darkness sealed away. because im pretty sure that in Blank points he said he wasnt gonna let the darkness take over him (so i think hes good)

namine cant control terras darkness, the only reason she could control riku was because he was a good friend of sora, because namine only has control of sora and his friends hearts.

What Namine meant by "locking Ansem SoD away" isn't simply blocking him out like a gate. Remember, her powers are only over memories, specifically the memories of Sora and those connected to him. What she meant was, while Riku is sleeping, she could be break apart the memory chains within Ansem SoD, the memories within the heart of Apprentice Xehanort. With his memories gone, he'd be in a similar state as the newly born Apprentice Xehanort, back when he had no memories and was essentially powerless. No memories = no power, so Rku wouldn't have to deal with the risks of using darkness and allowing Ansem SoD to surface and take control.