It is now an established historical fact that towards the end of World War II, the Nazis were in fact developing bizarre new weapons one after another, such as the V-2 rocket weapon, a mega tank called the "Maus," etc.
There were even plans for a weapon-like rocket fighter, which Japan, under military alliance with Germany, tried to complete using German research. (The project was never commercialized).
These events inspired Tezuka Osamu to craft the story of a fictitious secret weapon, Big X, which he portrays as jointly developed by Japan and Germany.
"Big X" was also produced for television in cartoon form, and both the Manga and made-for-TV animation versions became huge hits. Tezuka Osamu, however, was not too attached to his character Akira Asagumo, who came to represent an overly righteous hero trumpeting justice.
Despite such sentiment on the part of the author, the work became a leading satirical Manga, realistically depicting the terror of the war. No one else but Tezuka Osamu, who witnessed the war himself, could have produced such an effective piece of work. (Souce: tezukaosamu.net)