Tomura had decided to mindlessly wander through the dimly lit city, walking through and past many dark hallways with little to no movements nor noises

That was until he heard a ruffle, something moving. Curiosity took over him, and he decided to take a peek. He saw a small cardboard box

You were inside this box, a small and young puppy. You caused his gaze to soften, and his mind wander back to Mon, the dog he had dearly loved, the one who was there for him through his childhood