when it comes to new concepts how do they get ideas for it?
Once, a manga editor saw a note one of his creators had written that said “Grudge vs Ring was a cool movie”, and he essentially said “go off on that”. That’s how we got DanDaDan.
A mangaka wanted to make a horror battle manga. Since there was already a lot of fighting manga, he decided to focus on competitive games instead. That’s how we got Yu-Gi-Oh.
A mangaka wanted to make a death game series, but there was a gap in the market for casual romcoms instead. He then merged the two ideas together and had two tsunderes in mind games for romantic affection. That’s how we got Kaguya-Sama.
There is no method to making good ideas. It’s blind luck, flexibility and creativity, coupled with skill in executing whatever slapdash ideas you have.
what if a few ideas are incompatible?
What if you explored why those ideas are incompatible?
Like the idea of falling in love with a beautiful girl and dating a robot that you can never have sex with should be incompatible, but then you have Chobits.
The idea of being the only human in a world full of superheroes and becoming the world’s greatest superhero should be incompatible but then you have my hero academia.
Why would they need to be compatible? You don’t need to put all your ideas into a single work. Ideas are easy, so if an idea doesn’t work, change it or drop it. In other words, be flexible.
but what about drawing design?
What exactly is your question here? How to come up with designs? Same basic process that you learn by doing it.
The same way any artist does (which decidedly does not include asking a machine). It’s difficult to teach but the more you do it, the more stories your head generates.
An unfortunately more realistic answer is “look for what’s popular and copy that”. For every hit there are dozens of low quality imitators.
They exercise their creativity. They produce a bunch of ideas and choose the one they like best.
See: Draw This, Then Die! (or the manga it is adapted from)
