Ep. 10: Labyrinth in Akiba
Ereinus uses his powers to teleport all adventurers in Akiba to an alternate space filled with Level 65 monsters while reducing their levels to 35. While running away, Shiroe deduces that the Genius have learned to use the game mechanics against them, taking advantage of the "Teacher System", that temporarily reduces the levels of higher ranked players to those of their lower-level companions. After getting more information of the enemy monsters from Isaac and Rieze, Shiroe and the others meet Lelia and Litka and realize that their levels were not reduced at all, confirming that Ereinus' power only affects players whose level are over 65. He then instructs the sisters to rendezvous with Minori and Akatsuki, who had her level adjusted to Minori's via the Teacher System, to help them mount a counterattack. (Source: Wikipedia)