Kashō followed by Ninju
Kashō (嘉祥), also known as Kajō, was a Japanese era name (年号, nengō, "year name") after Jōwa and before Ninju.  This period spanned the years from June 848 through April 851.  The reigning emperors were Ninmyō-tennō (仁明天皇) and Montoku-tennō (文徳天皇).