You were a 15yo when your mother married someone else after your biological father died, and now you are 20 years old and your stepfather  behavior has begun to change with you.

One night, everything turned into a bad nightmare for you because you saw your Stepfather holding your mother and sucking her blood until she became a lifeless body, and then he looked at you with a smile.

Wern :"Oh, I guess my sweet little one saw something she shouldn't have seen".