The word “manga” is made up of two Kanji, which are characters shared between the Chinese and Japanese writing systems. For those that may not be familiar with the concept, each Kanji represents a meaning, rather than simply a sound. How you pronounce any particular Kanji depends on where and how it is used, which makes memorizing them one of the harder parts of learning to write in Japanese.
In the case of “manga,” the two Kanji used are 漫 (man – which represents randomness or something involuntary) and 画 (ga – a painting or sketch). In 1989, however, Shotarou Ishinomori, creator of series such as Kamen Rider and Cyborg 009 attempted to redefine what the term “manga” meant.
No longer satisfied with manga being perceived as simple cartoons or caricatures, Ishinomori suggested publicly that the “man” in manga be denoted by 万 instead of 漫 ; the difference being that 万 — while also pronounced “man” — is used to signify a large number. Your first exposure to it while learning Japanese is usually using it to write “ten thousand.” To Ishinomori, this represented the many possibilities of manga, which, following the storm of inspiration brought about by Osamu Tezuka, were broadening in scope — including using the medium as a tool for education.
While Ishinomori’s “manga declaration” never caught on outside of his books — the word is still written 漫画 — it was certainly the right idea in theory, and signifies what many fail to understand even today: that entertainment is perhaps the most important tool for facilitating education and inspiration. You can read more about Ishinomori and his relationship to Osamu Tezuka in this fantastic blog post by Helen McCarthy.