Gacha game
A is a video game that implements the (toy vending machine) mechanic. Similar to loot boxes, gacha games induce players to spend in-game currency to receive a random virtual item. The in-game currency can be gained by game play, or by purchasing it from the game publisher using real-world funds. Most of these games are free-to-play (F2P) mobile games, where the serves as an incentive to spend real-world money. The game model began to be widely used in the early 2010s, particularly in Japan. Most of the highest-grossing mobile games in  Japan use it, and it has become an integral part of Japanese mobile game culture. The game mechanism is also increasingly used in Chinese and Korean games, as well as Western games. Despite their popularity, "gacha" games have been criticized for being addictive, and are often compared to gambling due to the incentive to spend real-world money. Model. In these games, there are usually numerous characters, cards, or other items that players can obtain, and most of them are only obtainable via a "gacha" mechanism. This allow players to "pull" or "spin" the (analogous to a slot machine or  roulette wheel) using a specific amount of in-game currency, which will then give the player a randomized character, card, or other item. Sometimes, these are limited, such that specific prizes can only be obtained within a specific event time-frame. Because some of the rewards have a lower chance to appear, typically players must spin the many times before they get their desired outcome. Some gacha models use a pity system: that is, the player will be guaranteed an item after pulling for that item a large number of times without success. Soft pity increases the probability slightly of  getting a rare item with every pull, counting up and recalculating the probability until the rare item is received, while hard pity uses a counter to keep track of the number of pulls and automatically dispense the rare item after reaching a preset number. In many games, rewards are essential for players to make progress in the game. Players may be given free or discounted , but have to pay to get more. These games may also feature different tiers of pulls, which give different sets of rewards. The model of has been compared to that of collectible trading card games  as well as to gambling. An aspect of monetisation commonly found in the financing of games involves a model where a large part of the game's revenue comes from a very small proportion of players who spend an unusually large amount of money on rolls, essentially subsidising the game for other players who may spend smaller amounts of money, or even free-to-play players that spend no money at all. The high-spending players are often colloquially referred to as "whales". Types. Complete. , also shortened as "kompu gacha" or "compu gacha" , was a monetization model popular in Japanese  mobile phone video games until 2012, when it was found to be illegal by Japan's Consumer Affairs Agency. Under complete rules, players attempt to "complete" a set of common items at random in a particular loot pool in order to combine them into a rarer item. The first few items in a set can be rapidly acquired but as the number of missing items decreases it becomes increasingly unlikely that redeeming a loot box will complete the set (see coupon collector's problem). This is particularly true if there are a large number of common items in the game , since eventually one single, specific item is required. Box. Box is a virtual box of set items with known probabilities. Its popularity grew around the time that the complete controversy was becoming publicized. As items are pulled from the box, the likelihood of receiving the desired item increases since there are fewer items in the box. It is also possible to pull every item in the box, provided the player is willing to spend enough. For this reason, some players will calculate how much money it would take to ensure they pull the item of their choosing. Redraw. Redraw allows  the player to "re-roll" the if they receive an unfavorable result. Some games offer this feature for free. In games that offer an initial free roll upon commencement, players beginning the game for the first time may attempt "re-rolling" by repeatedly creating new accounts until they obtain the desired rare item or starting results. Trade. Trade allows the player to trade undesired items for a new roll that will give the player a better item. An example of this mechanic is "Need for Speed Payback". Consecutive. Consecutive improves the chances of receiving rare rewards when the player spends  in bulk. As opposed to spending a set amount for individual rolls, a player can spend a larger amount in order to roll several times in a row for a slightly discounted price. At the end of the roll, the player receives all the items at once. Step-up. With step-up , the player's chances of pulling a rare item is increased each time they roll. This is very popular with heavy spenders, because with every roll the stakes feel higher. Open versus closed. that show (open) versus hide (closed) the exact probabilities of pulling rare items. Discounted. Discounted  usually involve special campaigns or events by the game company to allow users to roll for a lower price. Appeal. Game developers have praised as being a great free-to-play monetization strategy. Most developers that work primarily with free-to-play games recommend it be incorporated into the game starting with the concept for maximum monetization potential. It has been debated what makes so addictive to so many players. Some believe that games play on the inherent hunter-gatherer instinct that people have to collect items, as well as the desire to complete a set. Others believe it is  simply the replication of the thrill of gambling that brings players back time and time again. Criticism and controversy. In May 2012, an article was published in a conservative Japanese newspaper, the "Yomiuri Shimbun", that criticized social networking games and specifically for exploiting the naivety of children to make a profit. The main complaint of the article was that the model too closely resembled gambling. The paper called for an investigation by Japan's Consumer Affairs Agency to prevent abuse of the system. Several cases of teenagers and even younger kids spending equivalents of over 1000 USD have been reported  in the media. Shortly after, the suggested investigation was performed and the model of complete was declared illegal by the Consumer Affairs Agency, citing the , The Consumer Affairs Agency stated that virtual items could be considered "prizes" under existing legislation written in 1977 to prevent the complete practice in the context of baseball trading cards. Within a month of the statement being issued, all major Japanese game publishers had removed complete rules from their games, though many developers found ways around this. In addition, several lawsuits were launched in Japan against companies selling gacha products, leading to temporary decrease in  their stock market value by almost a quarter. Japanese mobile game developers, including GREE and DeNA, worked to establish a self-regulating industry group, the Japan Social Game Association, which was an attempt to push developers from these models, but it did not prove successful, and the Association was disbanded by 2015. The mechanism has come under scrutiny for its similarity to gambling, and some countries require drop rates to be made public, or have banned certain practices (e.g., complete ). Many players also feel regret after making purchases in these games according to a survey. This type of game has  also come under criticism for luring players into spending thousands of dollars at a time to get what they want, and the way outcomes are presented within the game have also been criticized. Children are likely to be affected by the gambling-like mechanism since mobile devices provides easy access to payment; some game developers also intentionally introduce emotional manipulations and exploitive practices. A 2019 research paper has noted that "the gacha system has proven to be addictive and problematic" and speculated that the loopholes in the gacha system could be exploited for international money laundering. Gacha game A is