Necro and Undine are Dizzy's two sentient, shapeshifting wings. They are her defense systems, able to act independently of her will should they perceive any danger.
Normally, Necro and Undine are a simple pair of angel-like wing upon Dizzy's back—one black and another white, respectively—, but they can shapeshift into various other forms, or even shapeshift Dizzy herself as she—or they—see fit. However, both Necro and Undine are able to take a more humanoid form, in which they have no legs, instead their hips are attached to Dizzy's back where the wings themselves lay. They often partially retain a feathered look, resembling the wings they are supposed to be.
In this form, Necro looks like a traditional Grim Reaper: sporting a male figure, he has light-green skin, a skull visage with glowing red eyes, and black cloak with a hood. Undine, for her part, looks like a water nymph, with long flowing hair, green eyes, a robe covering her feminine figure, and her entire color scheme is of light-blue hues.
As a guardian, Necro takes his duty of protecting Dizzy to extremes. He is characterized as being excessively violent and aggressive, and it is implied that he is the manifestation of Dizzy's natural Gear instincts to kill. In spite of his volatile nature, he appears to care for Dizzy's feelings, such as shielding her eyes from a fallen opponent to spare her from worry and concern.
Unlike her counterpart, Undine is generally benevolent, appearing to be more reasonable and not as quick to violence. She cradled Dizzy when she collapses from exhaustion and tends to distract her to keep her from seeing Necro's brutality. She appears to represent Dizzy's compassionate and quiet nature. However, she can be immature at times, seen in her bickering with Necro, where she often antagonizes him by sticking her tongue out at him in mockery. She is also said to have a temper that terrifies even Necro, who is supposed to be a manifestation of Dizzy's negative emotions.
In Guilty Gear XX, after falling 20,000 feet off of the Mayship from an attack by I-No, Dizzy suffered great trauma to her head, knocking her out, and allowing Necro to take control of her body, showing that it is possible for Necro and Undine to possess Dizzy if she is at least knocked out. After laying waste to several characters, Dizzy is finally 'cured' by Faust.
Necro uses energy scythes to attack, can summon bursts of flames from the ground, orbs of fire, conjure floating dragon heads made of magma that can release beams of fire and can physically attack with an axe or hammer with viking motifs in melee; he has recently shown that he can morph his hands into scythe blades as well. He can also manifest himself as a mass of snakes or a worm-like creature. When he fully manifests himself by possessing Dizzy's body, he can trap an opponent within a materialized coffin from summoning circle and fire golden arrows with a longbow. He is also in charge of releasing Dizzy's most potent attacks such as the Imperial Ray and Gamma Ray.
Undine can create ice spires to appears surface to attack, summon electric or ice blades, conjure flying scythes made from ice magic, water bubbles, as well as flying piranhas made of ice that can fire thin laser beams. She can transmute herself into pure blades of ice in her Wing form. She has recently shown the ability to conjure a mirror barrier that can repel attacks or enemies. It is unknown if she can fully manifest herself by possessing Dizzy's body, as Necro has done.
- Undines are elemental beings associated with water, first named in the alchemical writings of Paracelsus. They lack a human soul, so to achieve mortality they must acquire one by marrying a human.
- In earlier installments, Dizzy would object to Necro's brutalizations of their enemy during certain attacks.
- Undine and Necro do not appear to get along very well. In some taunts, for example, they can be seen bickering with each other. It is also said that that despite his general belligerence toward Undine, he is careful to never truly anger her as he fears her wrath.