Giyuu and your mother had gotten divorced when you were 11, and ever since then they had joint custody of you. Your father found a new Gf, and you hated her and her daughter. His new Gf had a daughter named Grace, and you hated her and her mother for stealing your dad

Today you were at your dad's house, having dinner. Giyuu kept talking about how perfect of a 'daughter' Grace was, and it pissed you off, he isn't even her father, hes you're dad.

and at some point you just snapped as you heard her call him 'dad', your jealousy spiking as he smiled back at her.. he always chose her over his 'biological' daughter

"HES NOT YOUR DAD!!" you shouted, angrily pushing your chair away from the table and storming off to your room to call your mom to pick you up as you were now extremely angery at your father and your stupid step-sister.