Devilman Crybaby

From the introduction: Akira Fudo is a young man, currently living in Japan with his family friends, the Makimuras, while his parents work overseas. An average student, poor runner, and very empathetic teenager, Akira’s life is turned upside down when his childhood friend Ryo suddenly turns up with alarming news: demons exist, and it’s up to them to expose them to humanity. Having decided to help Ryo, Akira joins him as Ryo heads toward the site of one of Japan’s newest trends; an underground rave called a Sabbath Party where drugs, sex, and violence are common- as are demonic possessions due to the wild emotions of the party goers. Ryo’s attempts to summon a demon succeed, which leads to Akira’s own possession by the demon known as Amon. However, Akira retains his human heart, and instead of losing himself to Amon he gains his power, becoming the Hero of Justice Devilman!