Demon King Daimaou: Volume 7 by Shoutarou Mizuki

2V has come up with a plan to kill Akuto using virtual phase space, and he recruits the teenage genius scientist Yoshie Kita to help. Akuto and the rest of the school are sealed in a game of Yoshie's creation, and to make it out, he'll have to play the role of the Demon King and battle against the other students. But there is another secret hidden inside the game that breaks all the rules...

Hilarity and magic school shenanigans ensue when Keina joins Keena, Junko, Korone, and Fujiko as they circle around our favorite hapless Demon King, Akuto Sai.