Well... [Terra lapses into thoughtful silence; he has to think back for a few moments. The past few days have made his memory a little hazy, and pain isn't helping much, but he'll try and explain this in a way that makes as much sense as possible.]

The spirits called her the Bridge. She's the oldest of them all, and unlike CERES, she's filled with kind and good magic. That's why I wanted to help them.

[And maybe a little of the reason was the guilt that still haunted him about what he did to Princess Aurora. Saving someone else in a similar situation could be a way of making amends, even if he couldn't help the Princesses from here, but...]

I'm still waiting to hear back from the others who went in there. For all I know, she's still being held captive, and the entire raid was for nothing.