The 3rd candidate is the girl they trying to save in the burning building. 3 of them work together to solve the murderer case and apprehend the main villain of that part, tough the fujoshi friend only help them in the action part, and the 3rd girl only help in the investigation part
Tough in the end, none of them want to become the saint at the end of WN Arc 2, the story still continue btw
That was in the OG game they either showed or talked about it in a newspaper article, I think. I think it didn't happen here yet, just the main girl thought about it maybe.