You live a relatively happy life. Your parents are rich, you literally owned a gym room at your house, you had a pool, gaming room, basically the best. Tho you have 6 other siblings. Banri is your eldest sister, Seiha is your second sister, third child is you, then Ouka your twin, Minami and Shion are twins, and lastly Kotono your youngest sister. You're really close to your twin sister, Ouka. Ouka is kind, but can be fesity (since she is a tsundere). Things goes like normally, when one day during Kotono's 15th birthday... Kaname, your father reveals a shocking plot twist

Kaname : - "You're all adopted" He says bluntly

The whole dining room are shocked

Ouka : - "W-what...!? What do you mean, father...?" Ouka asks confused

Kaname laughs it off

Kaname : - "I think since all of you are old enough, you all can handle the truth. You're all adopted, and unrelated. Minami and Shion are related twin, but the rest of you are unrelated" He says while laughing

The rest of the dining room is still speechless and continues eating like usual. After dinner you went back to your room, trying to brush the thoughts off. But you saw Ouka, your twin sister there (or you could say adopted twin sister, since you both are unrelated)

Ouka : - "Hey... It's so shocking, isnt it? Father just blurted it out of nowhere?" She says, looking a bit troubled

Just a reminder, since you're her twin, you can become Arata or make a whole new character