A Forgotten Friend
Having spent his childhood in an orphanage, Arthur didn't have a lot of friends.
The children that lived at the orphanage weren't exactly from the right kind of homes, with most having been orphaned early at birth. This was the same case with Arthur, as his parents too had died when he was but just a toddler.
In fact, most of the children in the orphanage were the same as Arthur having lost their parents in the same disastrous earthquake. On some level, this was something that connected them as well as something that gave them nightmares.
Of course, even in the gloominess of the orphanage, Arthur still had a few people that he liked and was friends with.