headcanon. after finding out that he had been manipulated by ultear, jellal became concerned that it would happen again. not that ultear would manipulate him— he trusted her enough to know that she would never do anything like that again— but that someone else would.
ultear knew that the odds of that happening were incredibly slim, as she had only been able to sneak into jellal’s mind because circumstances had happened in a way that made it possible, but she also knew that the quickest way to make jellal more comfortable would to be to teach him how to guard his own mind.
now, jellal has mental defences that make it difficult to do anything with his mind— control it, read it, whatever. he is able to take these defences down when he likes, or to give certain people access.
currently, the three people who he has ‘unlocked’ his mental door for are erza, meredy, and erik.