How to make your own Doujin Soft game series?

I want to know how does some fans in Japan are able to make their own Dojin Soft game series because I'm going to japan after I finish college and I'm going to make my own series that could last more than just 10 years, it's a third-person bullet barrage game with hundred male characters (because female characters are cliche). Can anybody plz help.

And for those of you who are wanting to know my nationality, I'm a filipino boy who moved to Australia 4 years ago and I'm currently trying my hardest learning Japanese and improving my anime drawing skills.