He doesn't know why he wants to remember them; why he brings his camera around and takes a picture of their last moments before death, keeping them as memories forever. Some pictures turning out to be gruesome and disgusting messes that make his stomach churn, while other photos reveal those that seem more peaceful and happy, easily showcasing the differences between those deaths and those of the unwanted. 

That's the only differences in the souls that he collects, because unlike what most people think, all souls are void of color, are relatively the same size, and shape. Nothing about them tells the reaper what the person did before they died and he eventually came to collect their souls. He vaguely knows of their life from what is whispered to him in his ears, telling him when he needs to do his job, but other than that, he can never tell the difference between those that were good and those that were evil. 

But the pictures he had taken told him everything that he needed to know, showing him how they had lived and felt before they had died. The pictures that were peaceful often showed him a scene of someone smiling, glad to have their soul collected. While the more gruesome photos depicted various scenes of pain, destruction, and evilness, things he had seen too much of within his short life as a reaper.

Things he had never really known until he had died young and was taken pity on by the reaper before him, the being giving him his power and job as he was finally able to move onto the next life. The being leaving him to a torture that was made him more than jaded and cynical, transforming him from the happy-go-lucky kid he had been as a human to the dark and tired reaper he had became. 

Because nothing ever prepares one for the constant plague of death that follows a reaper, changing them in ways that no one would ever be able to bear, trapping them in this type of career that they can never quit until they find a successor. And even though Myungsoo goes around with a perpetual frown on his face and fuels myths and legends for years to come, scaring people until many literally fear death, Myungsoo can't help but be different than the other reapers around him.

He can't help but get this feeling in his chest that feels as if something is burning a hole through his nonexistent heart whenever he gets a new case, but someone documenting what he's doing and learning what he can about the souls he collects makes the burning feeling fade until it's gone until the next case comes by. And even though he doesn't really know what that means, doesn't know why he's the only one that gets that feeling, he can't help but feel that if he didn't have it, that if he wasn't different, then there would be something else missing besides the heart that hasn't been in his chest for the past twenty or so years. 

He knows he's young compared to the reapers around him, innocent and naive in a world that he didn't choose to live in and has to eventually resign himself to a fate that plagues reapers up to thousands of years before a new reaper takes their place. His age may even explain why he does what he does, why he has to document the souls the he collects, his reaper body still untainted by everything that goes around him and that it's only a matter of time until his little hobby becomes nonexistent and he goes around like all the other reapers that are doing their jobs.

He doesn't know and he doesn't know who he can ask to tell him why he does the things he does, why he feels the way he does, because for all the years that he has lived as a reaper, not one has communicated with him to tell him something he may need to know. He's had to train himself by using the voices that whisper things in his head, telling him what to do and who to kill and what soul to collect next. 

The voices don't sound evil as one may expect, because they're actually quite soft and breathy in a way that sounds good to his ear, making him want to act out the orders they tell him. And yeah, he doesn't know what would happen if he disobeyed them, but he has this feeling that he should never disobey the voices that plague him. Because not doing what he is told is fundamentally wrong and he would be punished for disobeying the commands that tell him when a human's life is expiring. 

And yet, they never say anything about the camera, never mention it whenever he brings it along and takes a photo before taking the person's soul out of their chest. 

So that must mean something, must tell him that it's okay for him to do what he's doing, even if it's a bit strange and he really has no idea why he's doing such a thing in the first place. But as time goes on and his jobs pick up, he can't bring himself to care too much about something so trivial when he has a job to do and the voices aren't telling him anything differently. 

He eventually forgets to wonder why he's taking photographs, because it becomes apparent that it's something he doesn't and will never need to know. Because it gets rid of the pain and gives him knowledge about things that he would have never known otherwise.

And by the time he realizes that for all the years that he's been a grim reaper, he has always taken pictures, has learned so much, that it means nothing when the voice disrupts everything that goes on in his head with one last call:

Find your predecessor. 

The camera and photographs that he's taken and collected throughout the years now mean nothing to him and will never mean anything to him again.