Tree of Qliphoth

The Tree of Qliphoth (クリフォトの樹) is a magic channel that connects to the underworld and allows devils to enter the living world. One of the Dark Triad's objectives is the recreation of this channel.

Overview
The magic channel branches out like the roots of a tree and descends to the seventh and lowest level of the underworld. At each level is a gate that normally prevents devils from moving between levels. Ten devils are set along the depth of the channel and are released as the gate to their level opens. Of these ten devils, the ones on the lower levels are stronger than the ones on the upper levels.

The ritual for opening this channel, known as the Qliphoth Advent Ritual (クリフォト降臨の儀), has two parts: a mage with World Tree Magic and a mage with Dark Magic in a magic circle combining their magic attributes, and three mages standing in positions along the perimeter of a larger magic circle. These three mages serve as activators for the ritual, so if they are defeated, the ritual will be halted. The ritual takes seven days to complete, at which point the World Tree and Dark Magic users will die.

History
Within the inherited knowledge of the Heart Kingdom's princesses, Lolopechka finds memories of a previous opening of the channel and the devastation it caused. The resulting destruction would devastate the entire continent and result in the massacre of 90% of the human population, bringing humanity close to extinction.

The Dark Triad of the Spade Kingdom plan to recreate the channel, so Zenon Zogratis leads an attack on the Golden Dawn squad in order to capture William Vangeance, while Dante Zogratis attacks the Black Bull squad to capture Yami Sukehiro. The two captains are brought to the Spade Kingdom, imprisoned in coffins, and placed in the center of a series of magic circles. As the ritual begins, the Dark Triad take their positions as the activators. An invading squad from the Clover Kingdom splits into teams that attack each of the Dark Triad with the intention of stopping the ritual.

Moris Libardirt uses the information he extracted from Lolopechka to develop a method for accelerating the growth of the tree. While the Dark Triad are fighting the Magic Knights, the first gate opens and two devils—Nahamah and Lilith—emerge, appearing in Dante's chamber. The roots of the tree stretch up into the sky and begin absorbing the mana from the world, while a horde of lower-ranked devils breaks out of the castle. With the gate to the underworld open, the Dark Triad members are able to access 100% of their devils' powers.

After Dante is defeated and knocked unconscious, part of the ritual's magic circle disappears, and the progression is slowed.

After all the members of the Dark Triad are defeated, the Qliphoth Advent Ritual continues, due to Morris having used his Magic to alter the Tree of Qliphoth so that it will continue to open the gates of the underworld without needing the Dark Traid. Instead, it now only needs for Morris himself to maintain the ritual, and the lives of Yami and William.

Trivia

 * The Qliphoth is the arrangement of evil forces in Kabbalah and is the opposing structure to the Sefirot, which was used for the elves' apostles and the tree of life monument.
 * The structure also resembles the nine circles of Hell from Dante's Inferno. In the poem, Satan, or Lucifer, is imprisoned on the lowest level.
 * Tabata accidentally drew the underworld as having nine levels instead of the intended seven. This is corrected in Volume 27.
 * Its depiction in Chapter 246 (and Episode 164) is based on Robert Fludd's illustration of the tree of life.