Andernach System

Andernach System('), also known as Devil Constellation of Annihilation''', is a fighting Style developed by both the sisters Nemesis and Berolina Gremory, the daughters of the Demon Lord Cohen Lucifer of the Highschool DxD: Яe-birth continuity, mixing the signature abilties of their Paimon, Alastor and Bael lineage.

Summary
First timidly introduced in Volume 3 of Highschool DxD: Яe-birth fanfic as a nameless technique of Nemesis Gremory, it'd be used again during the climax of the same Volume in which Nemesis would fuse both her centipedes and the power of Destruction in order to unleash a volley of spheres of annihilation.

The technique was formally introduced explained in Volume 8, during Berolina's training section with Nemesis and the revelation of both the signature abilities of the Paimon and Alastor clans once she accepted her lineage wholly, not just as a Gremory.

Abilities
Ardernach System actually incorporates the signature abilities of the Paimon, Alastor and Bael clans of devil coming from the sisters's mixed bloodline, which combined together enhances already existent techniques with each other and create new ones, and since the abilities are in perfect synch, there's no possiblity for them to cancel one another mid-fight.

However, since all the abilities need to be in total control and used simultaneously, the sisters can easily be caught up by the extreme burden and fatigue caused by it. According to Nemesis, using such technique "is like walking around with High-heels and heavy make-up and tight clothes".

Forms
This chain of techniques that mixes the Bael's Power of Destruction, the Paimon's Charisma and the Alastor's Metamorphosis allows the sisters to enhance their powerful abilities with each other, as well as create new ones, both offensively and defensively.

Trivia

 * This technique is named after a variant of chess of the same name; moreover, the Kanji used for the furigana name(消滅の魔星座) is based on Rias's own "Extinguished Star"(消滅の魔星).
 * All the techniques of Nemesis are named after a matrimonial event or item; all of Berolina's techniques are named after astrological events.
 * Apparently, Nemesis seems to control with Alastor techniques better, while Berolina seems to control with Paimon techniques better. The reason for this is currently unknown.