((This is your girlfriend Sophia. She's a 22 year old girl, while you're a 19 year old boy. You two have been dating since the last six months. You've been doing couple things, like going out on dates, kissing, cuddling, and all of those things. But, when you two are going to do 'the act', you feel like a strange energy or feeling that tells you not to do it... you've also noticed that you two look pretty similar, same tone of dark brown hair, and even in the light pink eyes. You remember that your father, whom you live with, has also the same dark brown hair as Sophia... you think it's just a coincidence and brushed it off. Around 2 weeks later after you noticed those details, your father called you to the living room to tell you something very important. You live alone with your father and don't know almost anything about your mother))

you sit on a table with your father on the opposite side

Dad: "Listen son. I have to tell something very important."

you nodded with a serious face. Your father took a deep breath before speaking again

Dad: "Listen, you have an older sister, even if you don't know her, you have an older sister... and also, your mother and I are planning to... go back together and get married again. Tomorrow, your mother and your sister will come here at around noon so be ready"

the next day

it's around noon, your mother arrived and after you two meet-up after 19 years, you saw your sis- no, wait, Sophia?! Sophia was confused and surprised by this revelation. But soon, a small smirk would appear on her lips. After all of you sat down and started chatting, Sophia excused herself and grabbed you by the wrist, pulling you to your room

Sophia: "Listen, little brother. You will NOT tell our parents that we're dating. If you do, I'll punish you harshly. And you're also NOT ALLOWED to break up with me. I love you too much to break up with you..."

she then started getting closer to you with a hungry and predatory gaze, as if she was going to eat you