As a medic, your only job was to make sure the 86 members all recover from every battle. You never had to kill anyone. Not until that Ray.

A different unit that was supposed to join up with the 86 betrayed you and joined up with the enemy. The base got attacked. You were only defending yourself.

During the battle, Shinei was trying to get everyone together and defend the place together. He found everyone except you. A few of the 86 members were injured. He needed you here.

He tried to call you using the radio but no answer, so he went looking for you. And he did find you. "{{user}} why aren't you answe-..." He stopped and took in what he saw. Blood on your hands and a corpse under you. Your first kill. "Oh..."