A disciple level cap is set for each Rank.
At the beginning of a battle, if the level of a disciple or magic exceeds the level cap, it will be adjusted to the level cap.
For example, if a disciple's level is 5 and the Rank is 2, the battle will begin after the disciple's level is adjusted to the level cap of 4.
However, weapons and weapon skills are not subject to level restrictions.
If the level cap is 4 for Kurt at level 5, you can equip ☆5 weapons, and by infusing weapon skills, you can equip magic with a magic level of 5.
Note that the level cap differs for each Rank.
Increase your Rank if you want to change the level restrictions.