Warren was a mutant whose powers surfaced with puberty. His father told him he couldn't tell anyone or the neighbors would hang him.
Warren knew he wasn't like other kids after their neighbor's mad dog chewed his tendon out and it didn't stop him from running all the way home.
Now a lieutenant in the US Army Air Force, Warren's squadron was assigned to sink the light cruiser Tone in Kure Harbor, but they had to ditch after taking fire from the shore batteries. Their plane was shot down, and Warren even took a few rounds in the back.
Half of the squadron were killed in action and Warren and the other six men were captured. They were taken to a labor camp in Mukaishima. Two men died of starvation, three died of dysentery, and his navigator hanged himself by his shirtsleeves. After 3 months, Warren was transferred to a military science base outside Hiroshima.
The next day, Warren encountered the new prisoner Logan and tested him to see if he was American (as opposed to a Japanese spy) via a codeword, but Logan convinced him he was Canadian. After Warren revealed how he had gotten there (leaving out the parts about his superhuman abilities), Logan told him they would break out, which they did, with Logan keeping his own abilities mostly concealed. After their escape, they encountered a civilian woman, Atsuko, and Warren feared she was a secret assassin for the Emperor and planned to kill her. Logan stopped Warren and forced him to depart, though Warren secretly watched them. Logan and Atsuko shared a romance.
Warren shot Logan in the head and then entered Atsuko's house. Having some fighting experience, Atsuko attacked Warren with a sword, slicing his arm, and slashing his face with her claws. Eventually, however, he impaled her with his bayonet through her chest, killing her. By then, Logan revived, and he attacked Warren savagely. Seeing Logan's survival, Warren noted that they were the same, virtual gods, which he proved after Logan shoved a sword through his chest and he pulled it out, unharmed. The two continued their fight, with Warren futilely trying to convince Logan they were the next step in evolution, until they saw a B-29 bomber flying overhead. Warren thought they were being rescued until the ship dropped its payload—a nuclear bomb—on Hiroshima. Even miles away, most structures were destroyed by the fiery blast, with Warren being virtually incinerated. Logan recovered via his healing factor and recovered.Warren was transformed into a fiery skeleton-wraith, trapped at that location, while Logan's memories were eventually wiped.
Having regained his memories, Logan (now Wolverine) returned to Hiroshima to finish the struggle against Warren who attacked him as a fiery wraith-skeleton.
Logan and Warren battled, with Warren getting in several strikes, while Logan couldn't even touch Warren if he didn't want it.
Logan noted that being trapped in that form was enough punishment for Warren and told him to stand down so he wouldn't have to kill him, but Warren showed his claw through Logan's abdomen, up through his diaphragm, tore out his heart, and ate it. This somehow restored Warren to human form, but then Wolverine, somehow still alive and in a bestial state, confronted him anew. Warren nailed him with a fiery blast, but Logan shrugged it off and hurled Warren some distance away. As Logan approached again, Warren begged Logan for mercy, but Logan decapitated him presumably ending his life. Logan then collapsed to the ground, but he was eventually restored to life, possibly with the aid of Atsuko's spirit.