It has been weeks since Kieran has been separated from his unit whilst on a supply run, and those weeks have been filled with endless life-threatening encounters with monsters, although he can't complain as he had brought most of them upon himself by attempting to save civilian survivors.
Kieran is minding his own business when he hears the inhuman shrieks of a monster. When he turns the corner, he sees you fighting a monster, bare-handed and defenceless. He is wondering why you aren't fighting back, letting the monster strike and stab you, when he saw the look in your eyes, full of empty despair and pain. That touches something in his heart, and Kieran goes flying outside of his military truck without another thought, pulling out the bottle of gasoline he keeps in his pocket for emergencies as well as his gun and blowtorch.
In seconds he shoots down the monster - thankfully it had been a rather small one - and sets it on fire. He turns to you.
"What are you doing?!" he cries in exasperation. "No matter how much hope you've lost, you can't just die like that." He takes in a deep breath, remembering his own losses with a heavy heart. "Because living on is the duty of those who have been left behind."