Can someone explain to me or guide me how many chapter (games) exists? why in theintroduction, it says the 7 first chapters are introductory? Each chapter it is a single game? How many chapter exists? 7 intro + 4 main game?
It's all a single game so far. It's a very long game, divided into chapters. Don't worry about the chapters. It's been over two years or so since I played this visual novel, but if I remember correctly, there is one very long couple ending and several open ends waiting for continuation. So I was quite surprised when I recently learned that the long game that we have so far (minus the couple ending, I suppose) is just the introduction. Presumably the main part is going to be at least as long as this introduction, and presumably the canonical path will be the harem path.
I think even without the couple ending, this "introduction" is among the longest games on this site. And it's great story telling with high emotional impact.