Why did Oriental Obsidian become Obsidian?

In the glory of the king's background story, it is mentioned that Obsidian's surname is Oriental, so it is also called Oriental Obsidian, so Oriental Obsidian is Obsidian's real name. Obsidian was called Oriental Obsidian when it was first put into use, but it was named Obsidian after it was officially put into use. In addition, Obsidian's sister mirror is called Oriental Mirror, and many of them are called Oriental Obsidian in formal clothes.