Yep, there are levels to x-ray.
Level 0 is a a joke one, showing only feet
Level 1 shows them without clothes but in their underwear
Level 2 shows full naked
You need to talk to Reina cause she gives you x-ray by completing her tasks of finding Jammers.
I'm pretty sure it's supposed to be a chained side quest and when you get LVL0 x-ray you are supposed to use it to find Jammer in the parking lot and bring it to Reina.
Then she will ask you to find the second Jammer, it will be in the Pool area, and the Third one will be in the Classroom.
Hope this helps!