Arbiters never remember the people they've judged.
It's so that their heads aren't filled with pointless information. At least, that's what Nona told him. Decim never questioned how the system works, it wasn't his place. His job was simple: Judge and repeat.
So, he would follow his orders and do his job. He would greet his customers, explain the circumstances, and have him play a game. He would judge them, and send them off to either Reincarnation or the Void. Then it would happen again, and again. Each time, he would receive the memories of his customers, and then he would soon forget them.
He would forget their face.
Their name.
Their judgement.
It wasn't like he needed to remember any of that. He would never see them again. But, even so, he started to dislike the idea of forgetting. Each customer had a backstory; they had lived their life to the fullest. They had made it through their share of hardships and depressions. So why wasn't he allowed to remember them? It seemed unfair that they would just disappear from the universe.
So, he started a doll collection. Gathering material was a bit difficult, but creating the doll itself was simple. He just used his threads to piece the doll together and form it like the customer that just left. He would leave them in the game room where they had gotten judged.
Slowly, his doll collection had grown. He would keep spare parts in the storage room behind it. It also served as an extra 'push' to have the customers play a game. If they hesitated, he would merely reveal the storage room. From their spot, the doll parts seemed like actual body parts.
Nona didn't like that he was wasting his time on such trivial things at first. She would keep remind him that his job was to judge and repeat. Nothing more, nothing less. Over time, she would get used to Decim's beautiful dolls, and no longer bothered him about it.
After a while, making dolls had become a habit. Soon after the customers left, he would create their doll. He had countless dolls, but he couldn't remember the names of any of them. It was better than not having anything to remember the customers by.
No doll was particularly special to him, he couldn't remember a single thing about any of them. And yet, there was one doll that made the edge of his lips slightly turn upward. She sat next to his bar, her ebony hair had a single white streak. Like all the other dolls, he couldn't remember a single thing about her.
All he knew, was that she made him happy.