Here is my 100% Achievement guide for Rainswept!
This is missable and it is for speaking to every single NPC on the first day.
In the video you see me talking to other policemen just incase, but i believe this begins when you enter the actual town for the first time (You know your in the town, as the game gives you options to open your map up etc etc).
So once you are here, keep your eyes peeled and talk to EVERYONE! There are only 5 or 6 people so it isn't bad, and this will unlock when you go down the street walking to your hotel.
Go to 17:15 to see the start and who i speak to to get this.
Hope this helps!