Hello! If you are reading this, you are a fellow fan of Haikyuu and I respect you! In this book, Kageyama not only has 1 twin but 2, both female, making him the only male in the three triplets. 

His first sibling is older than him by 5 minutes and her name is Seishin Kageyama. Her name, Seishin, means spirit which when you start reading, you will realize she mentions a lot. She is like Tobio but not like him at the same time. She can be competitive and rude or intimidating like him but she works as a teammate and believes that as long as you have spirit, you are a good person and that everyone has a spirit so everyone is a good person. Very wholesome but not very wholesome and she is called 'queen of the court' instead of King, but in a good way since she is co-captain and everyone likes her. She is 5'8, which is tall for a female especially a teen. She's really smart unlike Tobio and loves music but despises walking or running. Anything with strawberries she loves as well! She is friends with Oikawa and all of his friends, Oika-san and Sei-Chan~ She is also injured because of an accident in her past, so she has multiple scars on her right side of her face which she usually covers with makeup and her hair. She also has a weird mechanic brace on her right leg and right arm, which caused her abilities to slow down and for her to be worn down more. She also is very careful when choosing who to talk to, and she also doubts her own abilities. She doesn't eat much because of an eating disorder she has as well. She also wears glasses but wears contacts or nothing while in public.

Then there's Kikkukara. Her name I am pretty sure is not real because I have never heard of someone with that name but 'Kikku' means kick in Japanese and 'Kara' originates from the word 'Chikara' meaning force. So in short, her name means something along the lines of 'from the kick' or like "Force of the Kick" (I felt like such a genius brainstorming this name, but then like an idiot once I realized how dumb it was-). and she does not play volleyball but soccer, hence the name. She isn't dumb but she isn't smart, ya know pretty average. She is very upbeat and very energetic so she is different than her other siblings. Very likable and can become friends with literally everyone. She is besties with Oikawa, Oika-Chan~ and Kikku-Chan~. Lovessssssssssssssssss spicy stuff and loves to swim. She earned the nickname "Queen of the Field" Also in a good way. She is 5 solid, she got stuck on the short end of her genes since their parents are tall. She is also the youngest. She has some problems with her eyesight, as she is starting to lose her sight of color.

They all get along and get along with their older sister, yes older sister, Miwa (She is actually canon, I don't know if they show her in the anime but in the manga they do). They all occasionally play volleyball or soccer together and love it when Miwa has because she rarely has any time off her job. They all get along with their parents but they occasionally get mad at their father when he can't make it to their important games but got used to it. But basically almost a perfect family.

The three triplets constantly fight and are very competitive.

Either about who's strongest or fastest.

Kikkukara and Seishin about food.

Tobio just get's irritated when Seishin helps him with his homework.

Seishin and Tobio about if Volleyball or Soccer is better.

Miwa to tired to play.

So yeah! 

(Edited 12-9-2020: Added more details and spelling)