|This article is about a/an character in Kamen Rider 555.|
Ken Arai (新井 賢 Arai Ken?): A member of Ryusei School. Temporarily knocked out by Kawachi. He gained power and became obsessed with the Delta belt like many other users after using it. Along with Kyosuke, he kidnapped Mari to lure out Sawada to get the belt. Killed by Sawada. Ken Arai is portrayed by Hirohito Honda (本田 博仁 Honda Hirohito?).