Kyosuke Masaki (真樹京介, lit. Masaki Kyōsuke) is a character from Bad Company and Shonan Junai Gumi, the first leader of the Midnight Angels. When Eikichi Onizuka and Ryuji Danma were fighting the Skull Gang in Bad Company, he saved them and gave them back the motorbike the gang had stolen from them.
He originally founded the Midnight Angels with ten friends and became its first legendary leader. The gang grew and recruited new members. He was succeeded by Akutsu Junya, who became the second generation leader. He is the Oni-baku's idol, sharing with them his vision of Midnight Angel. He believes that Midnight Angel is not some cheap bike gang but they are Shonan's free roadsters.
He became good friends with a young Akutsu (second year of junior high) and became Akutsu's idol. He introduced Akutsu to the thrills of the world of the rider's world. He always reminded Akutsu to always ride with his heart and that Akutsu would get left behind if he was too slow. His attention was soon focused on Eikichi, much to Akutsu's jealousy. While drinking one night, he informs Eikichi that he wants Eikichi to take over.
After second generation Midnight Angel had grown to become the scariest gang in all of Kanagawa, an internal conflict separated the gang into three, resulting in the "Great Shonan War". He came out at the end of the war to declare Midnight Angel's end, heartbroken at what a monster Midnight Angel had become. A third Midnight Angel tried to resurface and he asked the Oni-baku to take them down and end Midnight Angel. He gives Eikichi his coat, telling him to wear it not to take over the world but to show his love for his friends and for Shonan. He asks the Oni-baku to never let Midnight Angel ride again and gives Eikichi his old bike.
Sometime after, he lost his life at a sharp turn on the old Odawara Highway due to an oil slick on the road, going further than anyone could ever reach and became a legend.
In GTO, Onizuka has a vision of Masaki when he's in a coma, telling him not to quit being alive and being the greatest teacher in Japan.