Citing a Video Game in Harvard Format Format
First, figure out what citation style you're supposed to be using in your Extended Essay, or if there is no particular recommendation, select one of the major ones and be consistent with it. That is, if you decide to use the Harvard style, use Harvard throughout your WHOLE essay and with every source you cite. Wikipedia doesn't have a house citation style, so what you're seeing there is going to vary from article to article.

You're spot-on with your research for the bibliography entry in Harvard style. You're also close with the in-line citation - just note that Harvard style doesn't use "chapters" there. Your reader doesn't need that information to locate the resource, so it isn't included. In your case, the in-line citation would simply be (Square Enix 2015a) or (Square Enix 2016b) if you end up citing 2 Square Enix titles. See here for another example.

If your teacher recommends that you use a different citation style, here are a few resources to get you started with citing video games:


MLA 
APA
Chicago


Final thought: don't worry too much about the particulars of the citation for something as unconventional as a video game. If the answer isn't immediately apparent to you with a simple Google search, it won't be to your outside grader either. They're likely no more experienced in academic referencing than your school librarian. And no matter how much time you put into your essay, they're still only paid to spend the absolute minimum time possible reviewing it... The last thing they're going to notice is a misplaced comma in your bibliography.

So focus your energy on the good stuff - the content - and just keep the rest consistent.