Mikoto's trying to enjoy her last day of summer vacation, but she is being stalked by Mitsuki Unabara, the Tokiwadai Middle School principal's grandson who's been chasing her since last week. In an attempt to make him give up, she pretends to go on a date with Toma. During their fake date, Toma learns that only 10 of the Sisters remain at Academy City while the rest went overseas for treatment. Toma converses with Unabara but is surprised to see another person who looks exactly like the latter running into a restaurant that Mikoto has entered. As the second and injured Unabara warns Mikoto about an approaching danger, Toma realizes that he is conversing with an imposter when the latter tries to hit him from behind. As Toma flees, Index reveals by phone that the imposter is using the magic of Aztec priests to disguise himself with another person's skin and wields an obsidian spearhead as a replica of the lance of Tlahuizcalpantecuhtli. When Toma is forced to fight him, the imposter reveals that he had been sent to become close to Toma's friends (such as Mikoto) to prevent the formation of the "Kamijo Faction", a group of mages and espers led by Toma which both the magic and science sides fear will destroy the truce between them. Since the imposter had fallen in love with Mikoto, he decided to protect her by killing Toma, but, now defeated and severely injured, he asks Toma to promise him to protect her since they'll be others like him after Toma and his friends. Unknown to both of them, Mikoto is listening nearby and is embarrassed to hear Toma's answer.