Overthrow the Tyrant Prince? No, Help Him Ascend the Throne

[The System ordered me to bring down the Crown Prince, but I became his sharpest blade instead] Su Tang transmigrates into a historical court-intrigue novel and becomes a cannon-fodder supporting character bound to the System. Her mission: overthrow the tyrannical Crown Prince and help the virtuous Prince ascend the throne. Looking at Xiao Yan, the Crown Prince of the Eastern Palace, rumored to be bloodthirsty and cruel, Su Tang smiles. The System tells her to hand him a knife? She turns around and puts the hilt straight into the Crown Prince's hand. “Your Highness, the virtuous prince wants you dead. I can prove it.” Xiao Yan grips her throat, his gaze sinister. “Prove it? If you can't, tonight will be your last.” She takes his cold fingers in hers. “If the evidence isn't enough, I'll help you fabricate some.” From then on, the Eastern Palace has a most unusual strategist. On the surface, she carries out the System's missions. In reality, she turns the tables and eliminates the virtuous prince's hidden agents. By day, she is a timid palace consort. By night, she is the Crown Prince's most secret blade. She helps him break deadlocks in the court's power struggles. When the frontier is in danger, she offers strategies to secure the realm. The System shrieks: [Warning! Host is assisting the mission target!] Su Tang replies calmly, “Look at it another way. Once he ascends the throne, I'll be Empress. Wouldn't it be even better if you worked for me, System?” Then one night, Xiao Yan pins her against the hidden door of his study, his breath burning hot. “I'll share half my realm with you. But it's time you told me all your secrets, isn't it?” She looks up at him. “What would Your Highness like to know? How I can foresee the future, or... that I chose you from the very beginning?”