Fade to Silence

Jin is an event based follower. When you are first exploring the zones the game will add an exclamation point to the map, and you'll be prompted that you discovered an event. You'll know this is Jin's event if you see smoke billowing from a large bonfire.

Jins event starts with you talking to him, three rippers will attack. Defeat them and then talk to Jin again. After a short conversation you can offer for Jin to join your camp, accept to get the achievement.

The followers who join you via events are somewhat randomized. Jin's event may take place in the Peaks zone, but for your play through another follower event could be there instead.