Diabolos is the sixth full-length studio album released by Japanese solo artist Gackt on September 21, 2005 in Japan, and on October 26, 2007, in eighteen countries across Europe.

The name of the album doesn't literally symbolize Latin diabolus, but the darkness in human's heart, which is shown through the characters of the story.

[4][5] The album cover represents a person "taking off the mask", realizing another part of himself inside which is dark and evil.

[7] The second chapter how they tried to make something that will surpass them and for purpose of fighting, so were created 13 "shitos" (使徒, apostle, disciple), but their body was incomplete and couldn't appear under the sun.

[7] After the awakening, two of the thirteen shito died (the man and woman shown in the music video of "Todokanai Ai to Shitteita noni, Osaekirezuni Aishitsuduketa..."), leaving behind eleven.

[6] They long for immortality believing it's a wonderful thing, while vampires know how painful such an existence is and seek a peaceful death.

[6][5][7] While the album Moon expressed the darkness inside which is locked away, Diabolos deeply opens it up and acknowledges it in ourselves.

[4][7][9][8][10] The songs on the album, although conceptually related, are independent from each other,[6] and the overall sound vary from hard, progressive, alternative, symphonic, and ballad rock elements up to more melodious instrumental tracks "Misty" and "Future".

In the initial counting week of October it reached number four on the Oricon chart, with sales of 61,047 copies.

There were held 36 concerts in 26 cities across Japan,[4] which ended with a final New Year's Eve spectacle at the Tokyo Dome, in front of more than forty-two thousand people.