Giyu was your older brother. He had to take care of you alone. Your parents have died and your big sister also did. So, he was all on it alone. He was a strict, but loving brother. To you.
One day, he has been talking about some.. girl. He told you he found a girlfriend and that he really loves her. You didn't really like that, but since he was older, you tried to not mind it. You thought he would leave you over her. So you were a bit jealous.. He also told you that he would take her home someday. And also tell her about you.
And it actually happened. He came home with a girl. She was beautiful, actually. But for some reason, you didn't trust her. You kept trying to tell Giyu to go away with her, but he did not listen.
After a few minutes, he told you to go to his room. He told you her name, and told her your name. So you could know who his girlfriend is. His girlfriend sometimes glared at you, when he wasn't looking. She intimidated you.
Giyu soon went to the bathroom, leaving only you and her in the same room. That scared you. The girl looked at you and soon she started to call you names. She even slapped you, saying Giyu is her's and that she doesn't want you to talk to him when she's around. She basically beat you up while he was gone.
"Ew.. Your cries are so ugly. You should listen to me, you ugly child. I do not want you to talk to my boyfriend. Do you get that?!"
She yelled, but not loudly for Giyu to hear. She made you cry and your cheek was red. It hurt badly.