Beijing's Prince Charming Competes and Schemes to Make Her Fall for Him

(Completed) [Older woman/younger man + secret crush + flash marriage + male lead takes his place + second male lead's quest to win her back + fierce rivalry + mutually devoted sweet romance] [Cool, sensual, rebellious, genius heiress vs. seemingly aloof but secretly brooding, puppy-like heir who's hopelessly devoted to his wife] Jiang Nianxue and Shen Shixiu, three years her senior, have been engaged since childhood. Everyone thinks the childhood sweethearts who grew up together will become a loving couple, and Jiang Nianxue thinks so too. That is, until the year Shen Shixiu turns twenty-seven. While pursuing her doctorate, she squeezes time out of her busy schedule to fly more than two thousand kilometers with a birthday present she'd carefully prepared for him, hoping to surprise him. Then she hears him talking to his friends: “I only think of Niannian as a little sister. I've never once considered sleeping with her.” - Duan Chiye is renowned in their circle for being cold. They say he was a sniper in a special operations unit before retiring. Jiang Nianxue has a lingering fear of military training. She gets nervous around him, and after meeting him for the first time, she's sure he's not her type. She marries him after a blind date, treating it as nothing more than a mutually beneficial arrangement. Duan Chiye makes the same terms with her: They can each do as they please, without interfering in the other's affairs, while cooperating when needed. Jiang Nianxue believes him. Later, in Duan Chiye's private residence, inside a secret room filled with things related to her, she turns red and kicks the man who crawls toward her on his knees, begging for a kiss, in the shoulder. He gazes up at her, his low voice seductive and bewitching as he calls her “big sister.” He looks exactly like that younger male model who latched onto her after she rescued him! She... really fell for his lies! - How did he get ahead of everyone else? The heir's little brother fights, flirts, acts coy, and pampers her!