I totally forgot the name of Aoba josai's Captain and also the senpai of Kageyama when he was in middle school.
That's Tooru Oikawa, occasionally called the "Grand King" (as opposed to Kageyama, the King of the court)
He is also a prodigy setter and Seijou's best player
His name is Toru Oikawa, commonly referred by the girls as Oikawa-senpai. They both went to Kitagawa Daichi middle school and were in the volleyball club. He's currently the captain of Aoba Jousai High School. He was the one who taught Kageyama his killer serve and how to block and spike. However, their tosses are of their own invention as he didn't teach Kageyama how to do it.