It's not OK to apply double standards in Emperors names in my opinion. We know Hirohito as such but we actually should refer to him as Emperor Shōwa since he's dead. Akihito will be Emperor Heisei.
Every Emperor is something-仁(hito) or 子(ko) if it's an Empress when he/she's living since at least 500 years ago.
However, the firebombing of Tokyo killed more people than any bombing attack in human history, including Hiroshima and Nagasaki.