With Asher Light guiding the pupils who had defeated the average-level undead with the might of a Lesser Demon. Yet, unbeknownst to them, there is a lurking peril that they could never have predicted. The three teachers only had enough time throughout their training to get them acquainted with lesser demons. Not because the teachers are incapable of summoning a higher-ranking demon, but because they need to improve their battle skills.
So the lesson about the difference in the strength of the devils was not exposed through summoning but just by feeling out the difference in the aura. Luther D'Arcy controlled his aura and emits the strength of each rank of the devils. So the students are capable of differentiating devils in accordance to their power. As for the characteristics of these devils, they were explained through verbal means as summoning it took too much time and resources.
