Good by Day, Bad by Night! Stop Flirting with Me, Yandere Little Brother

[Older woman/younger man + secret identities + sweet romance + five-year age gap] Cool and clever female CEO VS sweet, soft, adorable newcomer to the entertainment industry By day, she’s the young, bold CEO of the Lin Group, decisive and commanding. He’s a newcomer to the entertainment industry, with a sweet, handsome, sunny face and a healing smile. At night, she’s a darling who struggles to fall asleep, unable to face the shadows in her heart. He transforms into a tall, gentle sleep assistant who soothes her to sleep. By day, she’s his older sister; by night, she’s his baby. Her puppy-like boy is so sweet and flirtatious that the female CEO can only surrender, willingly sinking into the tender embrace of her sickly, possessive younger boyfriend, who’s both adorable and fierce. “Big Sis, if anyone bullies you, I’ll beat them up for you.” “Big Sis, if anyone bothers you, I’ll deal with him.” “Big Sis, if you can’t sleep, I’ll massage you and sing for you. How about it?” “Big Sis, can I... call you Baby?” She thought her sickly, possessive younger boyfriend had fallen for her over time. Who knew he’d been plotting this from the start?