When Kai almost 10 years old he had a sister went she was only 4 years old and her name was Hayakawa Seira and she only had her brother who went we are kids but right after she attends High School later that day Seira went home and saw that her brother is no longer at his room because she tells her mother that where is Kai Onii-chan go.
Seira: Okasan where is Kai Onii-chan went?
Mom: he went for business abroad a school for study for 3 years old in London, Seira-chan!
Seira: Okasan!! why did you do that and I didn't even say goodbye to him?
Mom: don't worry Seira-chan you can video chat
Seira: I didn't have his new number
She just went inside her room and lock herself in and she didn't eat or sleep Seira waited for her brother to came back home to see her.
Seira POV.
Kai Onii-chan please come to me and now I miss you so much whenever you are not around with me and at home, I can't contact you plus I didn't have your new number on my phone and I really if you come early I can't to hug you so tightly.
After 3 years later Kai went back home to his mansion first to put his belongings the night he went to see seira if she is happy to see me return home but I didn't send her a text or call her and I really need the number to contact to her.
Butler: Welcome back sir how is business abroad school like
President: well that abroad school hardly goes it looks but when I arrived there they are very friendly too
Butler: see I knew you could love it
President: I need to go see Seira-chan
Butler: sir about that she is now an idol and it called ''Nogizaka46''
President: my sister is now an idol did I miss something went I go to business abroad school
Butler didn't say a single word coming at his mouth but just nods his head at Kai when he leaves his mansion house and go to see Seira-chan at the Nogi studio and saw that she is so super happy that she smiles.
Out of a sudden, Kai went inside have walked around and someone noticed that good looking handsome guy just walk in and he is looking for someone is at here.
Himura: um...can I help you with something?
President: Himura Yuki-san, right?
Himura: yes, I am and who are you?
President: I'm sorry let me introduce myself my name is Kai Takeru and I'm Hayakawa Seira brother
Himura: Ahh!!! *hugs*
Later the captain of Nogizaka46 saw Himura with someone near the camera-san and she went there and saw who is he and why is he doing it here.
Akimoto: Himura-san who is he? did you know him?
President: of course he had a sister right here at Nogi studio
Akimoto: really? did he?
President: how rude of you to say like that, Akimoto Manatsu!!
Akimoto: how did you know my name was?
President: Manatsu I am back from the business abroad school that Hayakawa Seira is worry about me
Akimoto: wait...President?
Suddenly, Hayakawa Seira saw her Onii-chan is talking to Manatsu with Himura than she joins them too.
Seira: Kai Onii-chan!! I miss you so much *hugs*
President: I miss you too, Seira!
Himura: that call ''happy ending'' and Hayakawa Seira brother is happy by his side
Seira: yup I'm happy now and welcome back Onii-chan!!
President: I'm home
Hayakawa Seira grab Onii-chan arm and let them greet her brother to Nogizaka46 member and tell them that this is my brother who had away for 3 years to attend business abroad school and now he is back by her side forever.