Seraph of the End - Season 1 Episode 3 -

A student sneaks into the Forbidden Chamber, where the army keeps a demon for training. To show how dangerous a demon is, Shinoa takes Yuichiro and Yoichi there, but her plan fails when Yuichiro ignores Shinoa and starts to fight the demon.▽ Kokoro ni sumu oni [Japan: original Romaji title]▽ The Demon in Your Heart [Int'l: renamed English title]▽ The Demon Lives in Your Heart [Japan: literal English translation]