Yoru

Yoru is first shown to be very confident and prideful, treating her opponents as mere warm-ups and confidently vowing to take back the Nuclear Weapons Devil from Chainsaw Man. This might be a sign of her over-confidence as she lost to him previously while at full strength and is significantly weaker now. However, she is aware of her limitations and will back down from a fight if she believes the odds are against her. Yoru holds little sentimental value or attachments to humans, and is mostly uncaring of Mitaka's feelings, as evidenced by her blatant disregard for Mitaka's feelings of friendship for Yuko, repeatedly asking Mitaka to kill Yuko to use as a weapon or when she goes as far as to physically hurt Asa herself to forcefully regain control albeit with the intention of saving them both. She's been shown to be very cold and logical which clashes with Asa's highly emotional personality. Since she's completely unaffected by the Falling Devil, that means she easily gets over highly traumatic events such as being almost killed by Pochita and losing her power. Due to her predisposed nature as the War Devil, she keeps getting into conflicts with everyone around her, sometimes intentionally and sometimes not. Ironically these conflicts usually serve to hurt her. Later, Yoru devastates a whole city while using her powers and laughs maniacally when looking at the destruction she caused, reminding Asa that she, at her core, is still a Devil. Unlike her fellow Horsemen Makima and the Death Devil, who are almost always calm and composed, Yoru is more "human" as in flawed, immature and naïve. She is prone to losing her temper, and became embarrassed and angry at being rescued unintentionally by her archenemy, Chainsaw Man. In her anger, she sometimes throws childish tantrums by punching and screaming into the pillows on Asa's bed. She is very insecure and gets royally offended whenever her strength or intellect is questioned. Yoru is also worried about losing her power and being forgotten, showing a more sensitive side. Adding to that, she seems to show signs of sympathy, at least towards Asa. Yoru is able to form emotional attachments to others, such as her "comrades" whom she wants to rescue from Pochita's stomach, and the Gun and Tank Devils whom she considers her children and is hesitant to turn into weapons, even if she eventually does so. She is very content with eating basic foods like plain bread showing she isn't very demanding when it comes to physical pleasures. She does not have a good understanding of human society or relationships and takes things at face value, is easy to provoke and often threatens Mitaka with death. Though over time she grows closer to her and seems to understand and adapt to human society more, albeit she's still quite inept and will often unintentionally worsen her relationship with Asa because of that. Despite her apparent social-ineptitude she is very cunning in dangerous situations such as when fighting Devils and is easily able to keep a cool head unlike Asa. Though in the most extreme of circumstances Yoru will panic and scream out in fright, such as when Asa was caught by the Falling Devil. In rare moments, Yoru is willing to compromise her own safety and interests to avoid causing Asa traumatic grief, swerving away from Denji in order to not run over a dove tied to Asa's traumatic memories of Bucky. Despite initially keeping Asa alive just to weaponize her guilt and her constant manipulation, Yoru confesses her limitations, essentially calling Asa "arrogant" for feeling intense sorrow over doing what she needed to survive, reassuring Asa that the "sins" tearing her apart are insignificant to a Devil, and ultimately acknowledges Asa's feelings and helps her move past her deep-seated guilt.

Nightjar Fiend
Following the battle with the Four Horsemen and Weapon Devils, Yoru was also reduced to a “near-death state”, due to Pochita consuming most of her body. In this state, she claimed the body of a Nightjar bird, with its form changing to a beige-colored owl or potoo appearance with a piercing gaze. While her bird form is similar to Pochita's dog form, her true form isn't shown. The recognizable ringed Horsemen's eyes are also present in this form.

Yoru holds all of the standard Devil abilities, such as regeneration, reviving in Hell after being killed, restoring her health by consuming blood, fear empowerment and enhanced physical prowess. Despite being rather weak at the start, Yoru has the potential to become one of the strongest of the Four Horsemen, even strong enough to prevent the upcoming apocalypse. As stated by her elder sister, the Death Devil, Yoru in full power, is not only powerful enough to stop the apocalypse of her descend, but she is now able to make an apocalyptic scenario far worse than the one she wanted to prevent. Yoru planned to increase the world's fear of war, thereby restoring her power to its full potential. The Death Devil refers to this planned conflict as a "never-ending" World War II. Due to the California Governor's contract with Yoru, any fatal damage inflicted on Yoru is transferred to a random citizen of California. However, her contract with the Governor of California does not apply to self-inflicted injuries, as they cannot be offloaded onto American civilians. Yoru is also able to use a Contract Trigger ability because of her Gun Gauntlet.