He is introduced as a renegaded fighter who is spreading to the people of Tokyo Millennium that he is the true Messiah, and not Aleph. The Center, however, claims he is, in fact, the Anti-Messiah: a figure who predicted would oppose the will of the true Messiah. Both have numerous battles through the plot, where he becomes a sort of "recurring rival" for Aleph.
Daleth first appears after Aleph and Beth's missions, proclaiming to the populace that Aleph is a false savior and that he will prove himself by challenging him to a fight in Valhalla's Colosseum. Following the direct orders of the Center, Aleph and Beth confront him. In the ensuing battle, Beth takes cover for Aleph against Daleth's power attack and saves Aleph at the cost of her own life. Aleph spares Daleth's life, as to honor Beth's dying wish that both of the young men survive the ordeal. Daleth escapes, and the Center's Bishop, guiding a crowd of believers into the arena, cry out to the people that Aleph is indeed God's savior, and thus, the true Messiah. Daleth, on the other hand, swears revenge.
For the remainder of the game, Daleth appears in numerous different areas of both Tokyo Millennium and the Underworld, demanding various rematches that he loses. Finally, sheltering himself in the Shinjuku area of the Undeworld, a place under the control of the Oberon and various Yousei and Chirei, he befriends two demons named Puck and Hanoun, who help him in his plan to use Puck's "Fidelily Sap" on Aleph to make him fall in love with Hanoun and put him out of commission for good. The plan backfires, and the love potion affects Hiroko instead and she falls in love with Daleth. After Aleph forces Puck to give him the Infidelily Sap, he is helped by Oberon to break the spell on Hiroko. Daleth becomes afflicted with the sap and falls deeply in love with Hanoun, who also loved him. After this, Daleth abandons his grudge on Aleph, deciding to live in Shinjuku alongside Hanoun, in order to help the fairies make their lives easier. He also explains that the "Mars Pillar" Aleph picked up in one of their previous battles is one of the seven ancient artifacts needed to open a passage to the Abyss. He gives them a hint of where they can find the next Pillar before they leave.
If the player follows the Law or Neutral routes and defeats Lucifer, he will appear to inform Aleph that Kuzuryu is going out of control. During the ending on the Chaos route, he offers Aleph his gratitude for stopping the Megiddo Arc, and acknowledges him as the true Savior.
As with the other creations from the Center, the origins of his name is from the Hebrew Alphabet. He is named after the fourth letter, Dalet, also meaning "door". It is the equivalent of the Latin alphabet "D".