He Used Me and Now I Want to Run, but My Dream Guy Pins Me to the Wall and Kisses Me Senseless

[Both leads are romantically inexperienced + sweet romance] [Cold CEO vs. petite detective] Private investigator He Zhenzhen was caught secretly taking photos at a hotel and accidentally hid in a room. She never expected a handsome man to step out of the bathroom and give her an eyeful of premium content. Overcome with excitement, she snapped a photo. Only after escaping did she realize that the handsome man was her high school's heartthrob... She thought he wouldn't be able to find her, but he caught her red-handed at their class reunion. The richest man's illegitimate grandson still hasn't been found, has he? Just when she was stumped, a sticky rice dumpling fell from the sky! Luo Yichen: “Delete the photo!” He Zhenzhen: “Fine, but you have to help me with a little favor!” Luo Yichen: “What favor?” He Zhenzhen: “Pretend to be someone's grandson...” Threatened with the photo, Luo Yichen had no choice but to agree. What He Zhenzhen hadn't expected was that Luo Yichen would ask her for a favor too. He Zhenzhen: “What do you need help with?” Luo Yichen: “Pretend to be my girlfriend.” He Zhenzhen: “...Are you kidding me?” Luo Yichen: “If you don't want to go to prison for fraud and spend your days working a sewing machine, you have to help me.” He Zhenzhen: “Are you threatening me?!” Luo Yichen: “I learned from you.” He Zhenzhen planned to use Luo Yichen and then never see him again. She never expected him to lead her step by step into his home and put her name in his household registration book. He Zhenzhen: “Luo Yichen, you're really the richest man's grandson! So you've been plotting to get your hands on me all along!” Luo Yichen pinned her against the wall, his eyes full of affection. “You were the one who started it!”