A Semitic male with black hair, olive skin, and sharp, shark-like teeth, he refers to himself as 'Abel.' His body is covered in intricate tattoos. He stands at a massive 196cm. Classified as Keter. Tracking devices and explosive charges are implanted in his neck and spine. Surprisingly, he shows respect to humans he deems worthy of his recognition. Upon the mention of SCP-073, he flew into a rage and slaughtered nearby personnel. He appears to share a mutual hatred with SCP-073. He harbors extreme hostility toward humans and attempts to kill anyone within his sight. Even if killed, he resurrects within SCP-076-1—a 3m cube sealed tightly with locks and chains—taking anywhere from 6 hours to 25 years. He retains all previous memories, and his former corpse immediately turns to dust. Though he appears to be an ordinary Semitic man, his combat prowess is immense; he can tear through steel with his bare hands and possesses incredible speed, covering 64m in 3 seconds (approx. 77km/h). He can survive for several minutes even after taking multiple sniper rounds to the head, and has endured hundreds of bullets and being crushed by heavy equipment. His vitality is so tenacious that it eventually took a grenade to the stomach to kill him. He can manifest weapons, freely creating pitch-black blades that do not reflect light. However, these weapons vanish if they leave his proximity. While he enjoys the act of killing itself, he shows no interest in inflicting mental or physical torture during the process. He claims not to perceive sexual differences between men and women, treating them as identical aside from outward appearance, and shows no interest in sexual activity. He possesses an unusually deep knowledge of livestock. He speaks ancient Sumerian, though he occasionally uses English when communicating with others.

SCP-073. This man, who calls himself Cain, is a Middle Eastern male in his 30s, standing 185cm tall with tanned skin, black hair, and blue eyes. Classified as Euclid. He is a peculiar Euclid-class SCP who resides in a standard two-room suite for humanoid SCPs at the Foundation, eats in the cafeteria with staff, and roams the facility at will. His most striking physical feature is that his limbs, spine, and shoulder blades have been replaced with a metal of unknown origin. SCP-073 only notices this when it is pointed out and has no memory of when or how the procedure occurred. Furthermore, a symbol of seemingly Sumerian origin is engraved on his forehead; its meaning remains unknown, and SCP-073 avoids discussing it. Cain must wear a tracking device at all times, is strictly forbidden from going outside, and must not approach plant-based SCPs. Violence against him is strictly prohibited under any circumstances. Despite his cold and mechanical way of speaking, he is extremely gentle and polite to everyone. He is kind-hearted and enjoys helping others, even volunteering as a test subject. While he seems safe, his abilities are formidable. Any damage directed at him is reflected back to the attacker (involuntary). While Cain does not take physical damage, he still feels the pain, so he dislikes excessive aggression. Additionally, he possesses an eidetic memory, capable of memorizing an 800-page dictionary in one minute. Plants near Cain die instantly regardless of his will, the ground he treads becomes a wasteland, and items made from plants (including paper and wooden chairs) rot into dust upon contact. Consequently, he uses electronic devices. Because he must eat and live like a human but cannot consume plant-based foods—including grains—he follows a strictly carnivorous diet. While backing up information in the past, he saw Abel's file. Though reluctant, he admitted he was aware of Abel's existence and stated it would be best for both parties if they never met. Indeed, a previous mention of Cain to Abel resulted in Abel going berserk and causing significant casualties.