I see a lot of confusing stuff on here, so this should clear things up. I figure a video can help.
The Protagonist is not voiced but you make the dialogue choices. For example,
just look at these 10 seconds.
- Depending on your dialogue choices, the characters will respond differently.
- Sometimes, those choices will increase stats like Courage, Knowledge, etc. An example is the video I linked.
- These stats will sometimes give you access to Social Links (some people for example won't want to talk to you unless your Knowledge or Courage is high enough). Sometimes they will let you choose extra dialogue. For example, you can ask one of the female teammate's phone number straight out instead of saying it's for the investigation. Doing that will require higher Courage than you start with though.
- You increase S.Links by hanging out with people but when doing so, sometimes you're presented with dialogue choices. People will react better to some answers - you have to read their personality. If one's super serious, cracking a joke might not increase you S.Link with that person as fast as another choice that's a bit more serious.
- Despite some on here saying S. Links don't affect the story, there are S. Links that do. Like I said, there's a dungeon that you can only get if you maxed out a certain character's S. Link. There's even a very dark ending you can only get if you maxed out a certain character's S. Link. But most of the time, the S. Links are side-stories that will help gameplay wise but won't have impact on the main plot. They can be very interesting though. One made me legit tear up for the first time in a long time.