Born in 1953. Professor at Waseda University. Graduated from the First Department of Literature, Waseda University. Received doctoral course credits at Tohoku University Graduate School of Arts and Letters. Became a visiting professor at the University of Oxford in 2016. Mr. Arima is the author of such books as NHK Kaitai Shinsho (New Text on Anatomy of NHK) (WAC), Genpatsu, Shoriki, CIA – Kimitsu Bunsho de Yomu Showa Rimenshi (Nuclear Power Plants, Shoriki and CIA – Reading An Inside History of the Showa Era in Classified Documents), Genbaku – Watashi Tachi wa Nani mo Shiranakatta (A-Bombs – We Did Not Know Anything), Koshite Rekishi Mondai wa Netsuzo Sareru (Historical Issues are Forged in this Way) (Shincho Shinsho) and Ichiji Shiryo de Tadasu Gendaishi no Feiku (Going to Primary Sources to Correct Fakes in Modern History) (Fusosha Publishing).