Cao was born in S.1179.
A prominent intellectual, Cao is loyal to the Heiyue Syndicate. Most of his actions generally revolve around ways that would benefit his branch, even relying on authorities to do so. As such, others consider him to be a slippery, untrustworthy person, but his genuine loyalty to Heiyue means that he generally keeps his word to whoever he helps.
Despite being a skilled combatant, Cao prefers to leave the fighting to his subordinates, but he will partake in a fight if necessary.
Zero and Ao no Kiseki
Publicly seen as the president of the Heiyue Trading, Ltd. in Crossbell, Cao is actually a manager within the Heiyue syndicate. He came to Crossbell to break Revache's foothold and take over the underside of Crossbell. To accomplish his goals, he contracted the legendary Calvardian assassin Yin.
When he first met the Special Support Section, he surprised them by correctly telling them their names, ensuring he already has his intelligence network in place. In August S.1204, he was contracted by Samuel Rocksmith to protect him during the West Zemuria Trade Conference.
During the Red Constellation attack on Crossbell City, the Heiyue branch at the Harbor District was burnt down to the ground. Cao concluded it would be best to team up with the Special Support Section and work toward Crossbell's liberation. After the confusion in the city settled, Cao re-opened the Crossbell branch, which flourished with no rivals in Crossbell's illegal circuits.
When Crossbell was occupied by the Imperial Army, Cao helped Lloyd enter Geofront to claim some classified data before the Imperial government could.
Cao Lee eventually returned to Heiyue's Crossbell branch. He was later given a contract by the Crossbell government and given several archaisms to patrol Geofront Block X. He eventually cornered Class VII with the loaned archaisms, but was stopped by Elie and Estelle. Regardless, he had completed his side of the bargain.
He eventually appeared to offer help to Class VII and the SSS after the contract with the government expired, as he was solely interested in keeping Heiyue afloat, which would not be possible with the Great Twilight. He showed them a picture of McBurn and Victor S. Arseid at the top of Orchis Tower, and later had his associates help them set up a performance to distract the guards around the tower.
Cao entered an contract with Rufus Albarea, who simply wished to keep his branch afloat. He appeared to be aware that the Rufus that had come to speak with him was a fake, but continued to maintain his agreement regardless. After the Supreme Leader took over Crossbell, Cao kidnapped KeA Bannings and Ilya Platiere in the aftermath. Aware of Lloyd's recovery, he set up a trap at the Ancient Battlefield. Although the trap failed, he let KeA go for Lloyd entertaining his request.
When the rebels attacked the city, Cao deployed his branch to help the real Rufus, having been in contact with Dieter Crois and Garcia Rossi before their attack began. He claimed that the likely success of the uprising meant that his contract would be useless. After Project BABEL's Heavenly Thunder weapon leveled Juno Naval Fortress, Cao was unsurprised by its destruction, simply stating that the weapon was what the enemy had developed in secret.
Zero and Ao no Kiseki
- Crossbell Archive, p. 230.