When Yuuya reunites with the girl he saved back at the convenience store, she invites him to attend the prestigious Ousei Academy. Yuuya isn’t sure that he’s worthy of attending a school full of geniuses, but he’s persuaded to try it for just one day.

Yuya responds to Princess Lexia's marriage proposal and receives an invitation to an audience at the royal palace. At the same time, he returned to the Ôsei Academy.

Yuuya has found The Book of the Sage. As he reads it, he realizes that it’s even more amazing than it seems. Meanwhile, the class’s study trip draws near. Yuuya is at the department store with his friends to buy supplies when trouble suddenly strikes.

Yuuya runs across a girl fighting monsters in the Darkest Regions. She calls herself Luna. They begin spending their days training together, sweating side by side. Back at Ousei Academy, the off-campus study trip begins at a site deep in the mountains.

The study trip isn’t at all what Yuuya and the others had imagined. They’re faced with a series of unexpected challenges. Later, Yuuya meets with Lexia and her guards so they can escort him to his audience with the king, but Night begins acting strangely.

Lexia has been attacked, a crime punishable by execution. But Yuuya knows the would-be assassin and he can’t help wondering what could have caused them to do such a thing. The answer is shocking...as is the arrival of a new family member for Yuuya.

Reigar has been captured and must pay the price for his crimes, but Yuuya still has to deal with the enemy girl who proved to be just as strong as he is.