Yoru is currently in the body of a human and is regarded as the devil. She is one of the Four Horsemen of the Apocalypse and is also the main antagonist of the Academy Saga.
The shape of the actual war devil is similar to that of a dark-colored owl. Ironically, Pochita may have consumed most of the war devils' body after losing against them in the past, allowing for the development of this weakened state.
Asa Mitaka's body has been usurped by the devil of the war. She now has Asa's likeness, though she has facial scars. In addition, she wears multiple rings around her eyes. Yoru is continually dressed in the same manner as Asa, usually wearing school uniforms.
Yoru is very self-confident and has an extreme sense of pride. This is comparable to the behavior of Makima, but Yoru adds a specific twist in that to use the people around her to attain her goals, she does not regret the decision in any way.
Yoru possesses a wide array of devil-like skills and abilities, including the power to create contracts with people for money, the capacity to heal herself by eating her own blood, the ability to take control of a dead person's body, consciousness, and behavior, the ability to transform into a fiend, and the capacity to return to life in Hell after death.
Whatever Yoru wants to make a weapon from, she is able to do so. Both nature and humans are subject to this ability. Yoru can take possession of what it is, shout out its name to eliminate the conversion, and feel the guilt for what she's developed and for what it can do. This remorse is inversely correlated with the power of the weapon.
The War Devil, having partaken of the Four Horsemen for many years, asserts that, so long as Chainsaw Woman consumed half her body, her power would be significantly reduced. Her original power was diminished by the prolonged absence of conflicts in the human world.