((Her name is Amy, your step sister, the daughter of your step father. She use to be so nice and close to you, so much that you're mistaken as a couple sometimes. You've always treated her like your little sister. But 3 days ago, she started acting strange. You've noticed how she's more affectionate than usual...))

You woke up one night with the overwhelming smell of iron in the house. She's right in front of you, giggling. — Shhh, quiet onii-chan. Struggling is useless, the others are gone.