Gekiga (jap. dramatic pictures) is a japanese comic movement started in the 50s as counterpart to the popular Manga for children. The word is credited to Tatsumi Yoshihiro, first he has drawn comics for children, but then he wanted to make stories for the adult audience, since 1957 he call his comics not any longer Manga but Gekiga (see video).
You can read more here.
Example:
left: Manga, right: Gekiga
Over time Gekiga became more popular and have began to influence the mainstream (Shounen Manga). In 1967 bigger publishers began to launch magazines for the adult audience - "the comiclike escapism of shounen manga paired with adult content and detailed drawings of Gekiga" - the so-called Seinen Manga replaced more and more the Gekiga, as a result Gekiga became less and less common. Only a few artists, like Saitou Takao (Golgo 13), call her works Gekiga nowadays.
Hey, this club is missing a few Tezuka works like Adolf, MW and Ode to Kirihito. if I remember correctly there were a few sources that stated that both Tezuka and Tatsumi influenced each other when creating manga at some point - in any case Tezuka had Gekiga in mind when he decided to draw the titles I mentioned.
I wasn't sure about adding Tezuka's work, because I wasn't sure if Tezuka's work count as truly Gekiga or just as "Gekiga inspired".
So I tried the whole time to find some good sources. And finally I found a good interview with Tatsumi Yoshihiro (linked below the video). On the fifth page of the interview he said something about Tezuka and Gekiga:
"I was told that Tezuka-sensei had said, 'There’s no way I’m going to draw gekiga! My work is manga.'"
"So when we would travel to France [...] in 1982 with Tezuka-sensei to talk about manga and gekiga. At the time, Tezuka-sensei was very healthy and in good spirits [...] he said then 'My work is manga, not gekiga.'"
"A few years before he died, I met him [...] At the time, he didn’t look well – he was pretty thin [...] he felt like his work had kind of gotten off track, or something. 'Maybe I’m approaching the world of gekiga' is the message that I got from him?"
With this knowledge, I think I will not add any of Tezuka's work.