1. I think Kairi internalizes a lot of her problems, and dwells on things in private. If something bad were to happen, something so severe that she couldn't fix whatever happened, Kairi would likely dwell on it in private. She is the kind of person to put a brave face forward, especially around her friends or other people who are depending on her. She doesn't want to cause anyone else any undue worry, so she would try her best to keep herelf composed in public. In private, she may have more difficulties dealing with things. Confiding in close friends would help alleviate the grief of finding herself powerless again, as she spent so long being unable to do anything on her own. She would undoubtedly feel frustration, may even break down, but she wouldn't stay down forever. After a period of time, she would focus on what she could do, instead of dwelling on what she can't fix.

2. Keyblades have the ability to seal worlds, which means they wouldn't be connected to any others. If a world is unsealed, it would mean that travel outside of this realm would be possible. It probably shouldn't be allowed to do this, or else people would just be able to leave the setting.