Beniamino Cassano, dubbed the Devil of the Left Arm, began life as an abandoned child in the Tower's Middle Area. Sold with thousands of others to the Workshop for human experimentation to create Living Ignition Weapons, he became one of only two survivors out of 99,999 subjects, alongside Kang Horyang (originally Beniamino Ilmar). At age twelve, both were forcibly implanted with halves of a parasitic "devil" entity—Cassano receiving the left half and Horyang the right—becoming the Tower's first successful Living Ignition Weapons. Workshop researcher Sophia Amae raised them, providing training and maternal care while naming them. Cassano developed a deep resentment against the Tower's exploitation of the powerless, especially abandoned children, fueling his ambition to climb and reform the Tower into a haven for them. During events at the 28th Floor's Hand of Arlene, he lured Horyang under the pretense of reuniting with Sophia. Cassano then betrayed Horyang, ambushing him after a battle with opponents Ran and Novick. He stabbed Horyang through the back to extract his devil half, absorbing both entities into his own body and leaving Horyang comatose. Aligning with Team Rachel during the 30th Floor's Workshop Battle, Cassano secured the sentient Emile ignition weapon program from the Workshop. He delivered it to Rachel via a deal with the merchant Madoraco. Cassano later joined Rachel's group aboard the Hell Train, becoming a target of Wangnan and Team Sweet-and-Sour, who sought to retrieve the stolen devil half to revive Horyang. Confronted by Wangnan, who challenged the hypocrisy of sacrificing his childhood friend for a noble cause while condemning the Tower's cruelty, Cassano acknowledged Wangnan's perspective. As part of an arrangement with Rachel, Cassano departed the Hell Train at the 42nd Floor's Black Mountain station. His intent was to return to the lower floors, reunite with Horyang, and restore the devil half, signaling a potential shift from his earlier ruthless pragmatism. His abilities centered on Left Arm ignition, granting enhanced strength, speed, and defense through partial or full activation of the internal devil entity.