Unlike challenge stage 3, which had a group of enemies to worry about, stage 5 is more akin to a boss stage as it has only 1 enemy. That being said, there are a few gimmicks throughout this fight that you have to worry about.
The first being the cards that she puts on your students periodically. After it is applied to a student, it will detonate after 20 seconds, dealing damage and reducing their ATK, ATK SPD, EVA, and DEF.
Next, the boss will periodically move around the map, which can change the orientation of how your students are positioned. While this on its own is not a big issue, the boss has an AoE attack that can deal a large amount of damage to anyone near the tank. We recommend repositioning your tank to prevent the rest of your team from being hit.
Now onto team building for challenge stage 5, this stage does not have any mobs in it you will want to secure a strong Single-Target damage dealer to deal with the boss. In addition to this, you will also want to bring a tank and a Healer/Shielder that can reposition due to the boss’s gimmicks.
Note that characters listed here are only some of the viable options