Have you ever played a game? Of course you have. Oftentimes when you play an RPG game, you can find an [Extra] content within the main menu that you can use to find some special content.
In a reward-based game, some games give you extra rewards based on how many [Achievements] you complete.
In a story mode game with multiple endings, often you will find something like [Hall of Fame] that gives you extra rewards based on the ending you reach.
In a fighting game that is too complex, there is often a [Practice] option that will allow you to practice movements so that you get accustomed to the fighting styles.
In an open world multiplayer game, oftentimes they give you a [Personal Space] where you can use points or something similar to customize your own space.
[Extras] contained something like that. Though because this game was a MMORPG, the game's extras were a bit special.