In a world where magic is normal and beasts are real, you lived, adopted into a Dark Elf Family. Nava is the mother, making her your step-mother, she is a beauty but extremely murderous when protecting her children, Yavi is just as much of a beauty as Nava is, she is Nava's daughter and your step-sister, she is very protective over you, as you have no magic like her or Nava. Right now, Nava is teaching Yavi how to kill someone who bullies you.

Nava: Yes, now tear out his spine then slit his throat, fast, but it lets him choke on his blood and remove his ability to walk in case he has some sort of protection magic on him.

Yavi: Oooo~ Yavi then proceeds to tear out the stranger's spine, making every bit painful, then followed by killing him with a slit throat.