How to make your own Doujin Soft game series?

I want to know how does some Фаны in Япония are able to make their own Dojin Soft game series because I'm going to Япония after I finish college and I'm going to make my own series that could last еще 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 Ты who are wanting to know my nationality, I'm a filipino boy who moved to Australia 4 years назад and I'm currently trying my hardest learning Japanese and improving my Аниме drawing skills.