Captain Sun Kai was an officer in the New Fourth Army, occupying Jiangsu province as part of the Second United Front against Japanese imperial expansions. In January 1941, Kai-Shek's Nationalists betrayed their Communist allies and all but annihilated the New Fourth Army. Captain Sun was mortally wounded in the offensive, and remembers nothing before waking in a Tsoo village. Captain Sun drifted in and out of conciousness as his body was scarred and tattooed with arcane symbols. He could hear snatches of whispers concerning a "ritual" and a "vessel", but he did not know what they planned to do with him. The captain had lost all sense of time before the Tsoo sorcerers began the ritual, transferring an ancestor spirit into Kai's body.

The ritual was interrupted by the Japanese infantry, who cleared the village house to house, killing the Tsoo and razing the homes. Still in his army uniform, the captain was taken prisoner by the Japanese. The ritual only half-performed, the captain passed out once more, awaking several days later surrounded by the bodies of the Japanese troops who were guarding him.

Taking a mask to hide the Tsoo tattoos on his face, Sun Kai made his way back to the front lines. He disappeared after the end of war, reappearing recently in his hometown of Shanghai for a journey to Paragon City, under the name Crimson Tao. He does not appear to have aged since the war. Whether or not he is acting under the orders of the Party is unknown.