The materialisation of the Defense Program of the Book of Darkness. Although the name was first mentioned in The MOVIE 2nd A's, for convenience, also can used here for the "Darkness of the Book of Darkness" in A's TV version.
Nachtwal's Forms
Autonomous Form (基本形)
Multiple purple snakes.
Equipment Form (装備状態)
An equipment with chain at Reinforce's left wrist.