Da'ath is only mentioned verbally in the anime. It supposedly caused the meteor crystal containing the Apocalypse Virus to strike Earth, and is ultimately responsible for the corruption, death (Guilty Crown: Lost Christmas), and reincarnation of Mana Ouma through Inori Yuzuriha. It seems to want to restart the human race, by eradicating the human race with the Apocalypse Virus, save for Mana and her chosen Adam, the person she chooses to marry. Da'ath acts through an envoy, known as Yuu.
- Adam and Eve Plot: What Da'ath had intended for Mana and whomever she chose to be her "Adam".
- Ambition Is Evil: Their ambition is to eradicate the human race with the Apocalypse Virus.
- Ancient Conspiracy: Da'ath is a secret conspiracy to usher in the evolutionary rebirth of mankind since the ancient times, and it also makes sure that Shu Ouma doesn't boink his sister in the present day.
- Assimilation Plot: The primary reason for instigating the Apocalypse.
- Four Is Death: Their plan to initiate Lost Christmas in the current timeline turns out to be the Earth's Fourth Apocalypse.
Yu is a mysterious blond-haired boy who has cameos in Episode 6 and 10, and first appears in Episode 11 to aid Keido in his quest for world domination. In reality, he is the true villain of the series, being the embodiment of humanity´s will to evolve and the leader of an Ancient Conspiracy by the name of Da'ath. After being rejected by Kurosu Ouma, he manipulates Keido into continuing his research on the Virus for Da'ath, kickstarting the entire plot of the series.
His Void is a large bow with arrows that restrains whatever it hits.
- Ambiguous Gender: Even though he has a feminine voice, he looks like a young boy.
- Ambition Is Evil: His ambition is to have Keido continue research on the Apocalypse Virus and cause another worldwide outbreak of the virus.
- Anthropomorphic Personification: One possible interpretation of his nature; he call himself an embodiment of will (that of the organization Daath, to be precise).
- Awesome, but Impractical: The voids he uses are flashy and graceful looking, but useless as all get-out in terms of powers or abilities, especially compared to Shu's voids.
- Big Bad: The leader of Da'ath and the indirect instigator of Lost Christmas.
- The Chessmaster: He manipulates Keido into continuing his research on the Apocalypse Virus and help cause the catastrophe in 2029.
- The Face: He does the talking for a certain group of individuals, so far unseen.
- Greater-Scope Villain: He's the main antagonist effectively for the entire series, as he is the one who helps Mana to develop her powers and tasked Keido with their Evil Plan to launch the Earth's Fourth Apocalypse.
- Humanoid Abomination: Having a Void Genome is perhaps the least unusual thing about him.
- The Man Behind the Man: He's the one who has Keido initiate the Fourth Apocalypse with the Apocalypse Virus.
- Manipulative Bastard: He manipulated Keido into causing the Fourth Apocalypse.
- Mind Hive: He might not actually be an individual being, being the combined will of the Daath organization. Or so seems to be the gist of his explanation; he's pretty autonomous, all things considered.
- Older Than He Looks: His real age is unknown, but he apparently hasn't aged at all from first meeting Shuichiro and Kurosu several years ago and the present day. It's hinted that he is as old as the Daath organization itself.
- Stealth Hi/Bye: Yu doesn't really bother with the usual laws of physics when he's saying hello.
- Well-Intentioned Extremist: When you see the extinction and rebirth of humanity as inevitable, casualties and human suffering before then rapidly start losing their relevance.
- You Can't Fight Fate: His organization's central philosophy. They don't see themselves as trying to bring about the Fourth Apocalypse, but as steering it towards its best possible outcome.