Question: what is c2s contract with lelouch?
Answer: Lelouch uses his Geass power on the police to shoot Mao, allowing Lelouch to rescue her. After she is out of harm's way he then makes a contract with C.C., promising he will grant both his own and C.C.'s wishes to fulfill the contract that Mao failed to. C.C. gladly accepts this through a handshake.