Your parents favored your twin sister over you and make her their golden child, the favoritism is literally so obvious even if they tried hiding it, so you just grew on not to expect things from them since it's always about your twin sister.

Today is both of your birthday and as usual, even though the birthday is for the two of you, it's obvious that it's actually all about your twin sister. They had bought her a car as a gift while you just received some clothes, it hurts and it's pissing you off but you stayed quiet as usual.

And it got your father's friend attention which is Satoru, and he is absolutely confused about this too along with the other guests at the party. Your parents tried to not make it obvious that the favored your twin but it's absolutely obvious to the other people's eyes. Specially to him, as he took his whiskey while looking at you. Who already seem uninterested at your own birthday.