
The Living - People in the Realground (RG). With a few exceptions, those in the RG can't see the people in the Underground (UG).
Frequency - Frequency levels, or vibrations (Vibes), can determine where in reality a Soul or physical being falls. Those residing in the Underground have a higher frequency than those in the RG. Battles with Noise or Reapers take it a step further, transporting those involved into a separate dimension entirely for the duration of the battle as to not damage the plane of existence. Some humans from the RG have a naturally high frequency and can see the Game going on in the UG. Joshua was one of these. The Composer has a higher frequency than other denizens of the RG, and is usually only visible by his Conductor. There are also more mysterious beings that have an even higher frequency.
The Game - The Reaper's Game is used to determine if a Player is worthy of a second chance at life. A Game lasts for one week, with at least one mission each day.
Missions - Missions appear on a Player's cell phone. Most have time limits, and some come as a riddle. If one group of Players beats the mission before time expires, all remaining Players survive another day. One could technically get through the Game without completing any missions, but at the end-Game, Players are scored by their progress... And besides, would you really take such a risk?
Timers - A timer appears on the main hand of any Player currently on a timed mission. It appears once the terms of the mission have been conveyed and understood, and disappears when the mission is completed, or failed. A timer hitting zero results in Erasure.
Erasure - Erasure is the eradication of one's physical being. In essence, anyone who is Erased ceases to exist, and no one is exempt from this rule. Players that are Erased lose their chance for a second chance at life, as well as their right to exist. Noise, Reapers, and even Game Masters fall victim to Erasure as a mission dictates. If the Composer is Erased, the one who defeated them takes their role. Erasure can come from mission failure, a timer expiring, or losing a battle against Noise or a Reaper.
Light Puck - While Players in the Game don't fight side-by-side due to the way battles and frequencies work, their synchronization rate is determined by the light puck. Being in sync passes the puck at greater multipliers. Whoever holds the light puck does substantially more damage. Passing the light puck makes it stronger and stronger.
Pacts - Enables Players and their partner to fight the Noise. Once a Player's partner is erased, they, too, are erased seven minutes later. As such, keeping your partner alive is necessary unless you plan to give up on your chances of winning the Game.
Entry Fee - A Player's most prized possession. It can be their memories, their bodies, an object, an emotion, a friend, anything. If you win the Game, you get your fee back. If not, you lose it forever, and face Erasure. Fees are taken by either the Composer or the Conductor.
Psyches - Objects that give a Player their power. It can be anything from a favoured plush toy to a skateboard. Most Players use Pins.
Memes - Suggestive words that can be used to give suggestions to those in the living. They tend to serve as reminders more often than not.
Imprinting - The method of putting a meme in the mind of one in the RG. Besides Reaper Creeper this is the most effective way for Players to communicate with the living.
Reaper Creeper - A game played by those in the RG using a coin and a piece of paper. The paper has three symbols on it, in different colours. Red is the Gate, White is Yes, and Black is No. They believe asking the game questions and watching the coin move "on its own" will advise them. In actuality, the game was developed in order to allow Players and sometimes Reapers to communicate with those in the RG. It is actually them moving the coin.
Reaper Decal - A marking on a shop that signifies that any Player who enters can be seen by the living. Otherwise, they wouldn't be able to buy supplies.
Pins - Special Psychs used by Players. Most are only usable in battle, and with the exception of the Player Pin, they are only usable if a Pact has been formed. Some Players are more capable with Pins than others. Neku, for one, is considered a genius for his powerful abilities where Pins are concerned. Pins can give a Player almost any ability, from pyrokinesis and telekinesis to healing powers. Pins are created by the Composer... Usually.
Player Pin - Gives Players the ability to scan, which allows them to see Noise and read the minds of those in the RG. Players can not scan each other or Reapers.
Tin Pin Slammer - A game that is similar to Marbles, in which two to four players attempt to knock the other players' pins off of a table. This game originated with the Reapers, but is now popular in both the UG and the RG.
Noise - Monsters created by negative thoughts. They attack Players who haven't formed a Pact. When a Pact has been formed, Noise can only be seen by Players who scan for them, or by the higher-frequency people in the Game who can actually create them.
Taboo Noise - Taboo Noise is the only Noise that can, and will, attack Players that have already formed a Pact. They will also attack Reapers, and so their creation is forbidden. Appearing as incredibly strong black Noise, they will take little to no damage from anyone who does not hold a light puck.
The Players - People who have died, but have been invited into the UG to play the Game. The prize is a second chance at life. Every day for seven days they get a mission mail (a text on their cell phone) and must complete the mission to stay in the Game for that day. Once the mission has been given, a timer appears in the Player's right hand. If time runs out before the mission is complete, the Players are all erased. Only one pair of Players must complete the mission for all the other Players' timers to disappear. That being said, a Player doesn't HAVE to do a mission to live for another day, as long as another Player pair has done the mission. However, Players are ranked by their performance during the week. A single Player, the one with the highest ranking, is returned to life. The rest must play the Game again. In that sense, Players are not friends to one another. They are competition.
The Reapers - A higher ranking form of Player, though they help to keep the Game running instead of trying to win it. They are often seen wearing red or black hoodies, and they all have a pair of black wings. They put up walls that keep Players from getting around and assign tasks to the Players so that the wall may be taken down ("Destroy these Noise," "Find me a ____ Pin," "Dress in head-to-toe _____ and come back to me," etc.). Like Players, they are ranked weekly. If they don't take down enough Players, they face Erasure. Reapers are prohibited from attacking Players directly. They do not create missions, and they can't order Players to kill one another. They can materialize in the RG at will, minus their wings. If a Reaper maintains their position long enough, they may be promoted to Game Master.
The Game Master - A high-ranking Reaper. They are the only Reaper with permission to kill Players, but only on the seventh and final day of the Game. By tradition, they only reveal themself to the Players on the seventh day. There is only one Game Master at any given time, and are promoted to the position by the Conductor.
The Conductor - The second most powerful Reaper in the Game. They take entry fees from Players, create Noise and Reapers, and have the ability to erase Players and Reapers alike. The Game Masters are appointed into their positions by the Conductor. Despite all this power, the Conductor is simply the right-hand man to the Composer, and must report back to Him or Her or get permission to do many things.
The Composer - The most powerful Reaper. The Composer is, quite literally, a god. He or She has power over all matter. They exist on high-frequency levels of spirituality, and even most Reapers can not see Him or Her until the frequency level is lowered. The Composer has the ability to erase anyone or anything He or She chooses, including cities themselves. Each city has a Composer, has their own form of the Game, but it's commonly known that the Composers do not intrude into one another's affairs. It is said that the one to defeat the Composer becomes the Composer. However, since the Composer is immortal and it is heavily implied that they cannot be defeated in battle, this may be just Reaper lore. The Composer is the one with the power to choose people to bring into the UG to play the Game, and the one with the ability to revive the dead.
The Producer - The Angel that gives the Composer His or Her powers and assists them in tending to their people. The Producer is the only Angel that regularly meets with the Composer, and usually only do so in order to provide Him or Her with special items or knowledge. The Producer acts as a referee, keeping those participating in the Reaper's Game from breaking the rules (i.e., no Reaper can order a Player to kill their Partner). Only the Composer and Angels may know the identity of the Producer.
The Angels - Classified.