Thank you all for taking the time to answer my question.

My process is really simple: I picked the colors from the original with the color sampler from my editor, then placed every pixel by hand, keeping the original image open as a reference. I did not try to recreate the original, just an astronaut with the same color scheme.

Besides, this color scheme being found only on the Italian version, I'm not even sure it was colored by Osamu Tezuka himself, so I don't really know who to credit for the inspiration...

I started some concept art, and got stuck at that stage, here it is, I'm not sure if it qualifies: https://opengameart.org/content/diesel-punk-soldier-concept

Might be a little late to the party here, but anyway, here's the JavaScript frameworks I know of:

Phaser is a largely used game-engine full of features. This is what I personally use.

Kaboom is its direct concurrent with a different style of code.

LittleJs is a tiny engine made so you can read its source code and hack it.

RotJS is sepcifically aimed at making roguelikes.

CtJs is a game editor with all sort of tools to help you make games.

All of these can be run directly in a browser, but if you want to target other platforms (mobile or desktop), you'll have to add tools to convert HTML5 into executables, but it's still doable.

If you want some tutorials on Phaser or Kaboom, I can recommend Ourcade Tutorials and Code with Anya Kubow YouTube channels.