Beast Beneath the Moonlight gives Atsushi the ability to transform into a white tiger. At first, he did not seem to have much control over the transformation, likely due to the fact or caused by his unawareness of his state as an ability user.
- Full body to partial transformation: Atsushi has shown several varying states of transformation, which range from a rather large full tiger form, to just slit pupils and tiger stripes on his face. He can transform and manifest various tiger body parts at wills, such as tiger forearms with claws or a tiger tail.
- Regeneration: Also notable is that Atsushi's ability has extreme regenerative powers capable of healing bisection and amputation almost instantly. This was shown during his fight with Ryunosuke Akutagawa.
- Increased speed and stamina: He has shown to possess immense speed, durability, strength, stamina, and endurance on several occasions. He has also been shown to be a natural fighter in close combat and has shown to very cunning in battle in several fights. However, after using his ability, Atsushi seems to become unconscious and collapses onto the ground.
- Enhanced senses: Due to the tiger's nature, Atsushi can hear and see above what is normal for humans.
- Beast Beneath the Moonlight: Half-Human, Half-Tiger (月下獣・半人半虎, Gekka-jū: Hanjin Hanko?): Atsushi can transform into a partial tiger, this makes Atsushi to have the tiger's legs as his arms and feet. His eyes have slit pupils and he has tiger stripes on his face.
- Beast Beneath the Moonlight–Rashomon (月下獣羅生門, Gekka-jū Rashōmon?): Atsushi is wrapped by Rashomon.
- Beast Beneath the Moonlight–Rashomon: Toramurakumo (月下獣羅生門・虎叢, Gekka-jū Rashōmon: Tora Murakumo?): Atsushi's tiger claw is wrapped in Rashomon and enhances its offensive power, enough to overwhelm a fully-powered Francis Scott Key Fitzgerald.
- Beast Beneath the Moonlight–Rashomon: Black Tiger's Supreme Claw (月下獣羅生門・黒虎絶爪, Gekka-jū Rashōmon: Kokko Zessō?): Using the tiger's claws that can cut through abilities themselves and Rashomon, Atsushi can stretch out that severed space and cut through physical armor and abilities. It morphs into a divine blade, and as such, according to Akutagawa, no life form that suffered an attack from it can quite possibly survive.
- Spatial Distortion (空間 断絶, Kūkan Danzetsu?): Atsushi can distort a space resulting it to being crushed.
- Teleportation (瞬間跳躍, Shunkan Chōyaku?, literally "Instantaneous Leap"): Atsushi can teleport using the tiger's claws and Rashomon's power to cut through space.
Beast Beneath the Moonlight is a reference to the real-life Atsushi Nakajima's short story, The Moon Over the Mountain (山月記, Sangetsuki?). Based on a Tang dynasty legend of a certain Tiger Man, the story tells the encounter between a government official named Yuan Can and a man-eating tiger. The creature turns out to be his friend, Li Zheng, who himself believes has wasted his talents due to his fear of failure. He admits that his "cowardly pride" and "arrogant shame" eventually transformed him into a man-eating tiger.
This short story also became the namesake of another book entitled The Moon Over the Mountain: Stories, a collection of nine literary works that revolve around folktales, legends, and stories related to Ancient China.