Blackberries and Wolfsbane (Isaac Lahey)

Zorina "Zora" Stilinski is the younger twin sister of one Stiles Stilinski. She is the best friend of his life-long crush, Lydia Martin despite having a very similar personality to him, just as hyperactive, just as impulsive, just as sarcastic, and just as mischievous. The night before their sophomore year in High School, the three go to look for a dead body and are separated, Scott is bitten by a wolf and their lives change forever.

This is an Isaac Lahey story but it might take a while for him to appear

Season one and season two

Isaac Lahey x Stilinski!Sister Slow Burn