Shirō Ishii.
In general I notice a conspicuous lack of figures from that era of Japanese history in this thread.
I'd argue that Kishi Nobusuke, who became a postwar PM and whose immediate descendants are still politically relevant today, was, if not "more evil than Hitler", at least similarly evil in his public capacity to most similarly situated Nazi occupation functionaries, with his singularly unpleasant personal life larded on top of that. Obviously the primary responsibility for Japan's much more toxic attitude towards its past than Germany's lies with the Japanese people, but GHQ deciding not to insist on points like this certainly didn't help.
Kenji Doihara is honestly probably the most evil person in the Japanese military environment of the time period, though there is very tough competition.
Poll
