There are particular locks and chains that are used to seal up the Inner Temple of Hazakura when a spirit medium is training. They're called "trick locks", and can only be unlocked by the person who set them because there are literally hundreds of possible combinations to them.
The case doesn't really get into detail about what they're made of, but one thing is clear: They aren't ordinary locks. Iris placed one on the temple door to seal Maya in for training, but when Phoenix came back later to investigate, Dahlia had placed four more. There were no extra locks anywhere near the temple; even if there were, Dahlia wouldn't have known where to find them. So it stands to reason that these locks are summoned by the person who places them. Obviously this takes a bit of spiritual power, but Iris and Dahlia are only said not to be spirit mediums; as members of the Fey family, they have at least a little, even if it's not much.
Aside from being summoned psychically or whatever and being almost impossible to unlock if you aren't the one who set them, the locks are completely ordinary. They look like Psyche Locks, for those who know what those look like, but they're physical locks and chains that lock up doors, windows, and the like, and can be broken with enough physical strength.