Episode 15

Act of Kindness (やさしい事) is the 15th episode of the Ao no Exorcist anime overall and of the first season. It first aired on July 24, 2011.

Synopsis
Rin and his classmates succeed at the task given to them by their teachers, but the camp is attacked by Amaimon, who holds Shiemi hostage. Rin goes to save her when suddenly the others come. After his friends are beaten up, Rin has no option but to go full force against Amaimon. Rin is forced to reveal his secret by exposing his true form in front of his classmates.

Manga & Anime Differences

 * In the Manga, Rin Okumura accidentally cuts down one of the paper seals on the bridge, whereas in the Anime he knocks over one of the pillars.
 * Mephisto Pheles steps in between Rin Okumura and Amaimon's fight to stop them, with Amaimon throwing Mephisto into a tree before he uses Kuchens Kuckucksuhr to capture him. In the Anime, he simply waits for Amaimon to be knocked into a tree before unleashing Kuchens Kuckucksuhr.
 * In the Anime, Kuchens Kuckucksuhr is destroyed by Rin Okumura while he is on his rampage, where as it simply disappears at Mephisto Pheles command in the Manga.