Slap Fight

Slap Fight is a science fiction-themed vertically scrolling shoot 'em up game reminiscent of B-Wings, where players assume the role of an Allied League of Cosmic Nations (ALCON) fighter pilot taking control of the SW475 space fighter craft in a counterattack effort to defeat an invading alien race led by Gaudy on planet Theron as the main objective. Besides some stationary helicopters with blades spinning, there are no flying enemies in the entire game. As far as vertical scrolling shooters go, the title initially appears to be very standard, as players control their craft over a constantly scrolling background and the scenery never stops moving until a boss at the end that must be fought before progressing any further is reached. By default and without power ups, players have only a standard shot that travels a max distance of half the screen's height.

The game's weapon power-up system takes inspiration from Gradius; certain enemies spawn a star-shaped item upon destruction to be collected, activating an upgrade menu at the bottom of the screen that moves a lit cursor through the list of weapon power-ups described below. Activating any weapon power-up (apart from the side-shot), however, increases the ship's hitbox, making it a bigger target for enemy fire and difficult to keep successive lives in the heat of battle. If any power-up is lit but the player's ship is destroyed before a power-up could be selected, the star item is "carried over" and the speed power-up is lit on the next life. A number of hidden bonus secrets to be found are hosted, which is also crucial for reaching high-scores to obtain extra lives, as firing on determined locations and certain setpieces within the scenery in some stages reveals a bonus secret.

The plot of Slap Fight varies between each region and version. The game takes place in the year 2059 on another galaxy, mankind has colonized an alien planet called Theon after evacuating a previously colonized planet Orac. Five years ago, the colony on Orac was attacked by alien invaders and the war was so intense that the colonists were forced to leave. Theon is now under attack by the same alien fleet, but the humans are ready. The player assumes the role of an Allied League of Cosmic Nations (ALCON) fighter pilot in the SW475 space fighter craft to stop the invaders from taking over Theon.

Slap Fight's development team had a concept for a game that featured secrets, while its main appeal was to keep players investing in long play sessions that revolved around hidden items and the weapon power-up system, as then-Toaplan composer Masahiro Yuge stated that the team's idea for the game was to add as many secrets as they could such as an alien that resembled one from Space Invaders, which they included as an homage to Taito, with Yuge citing his affinity for titles with hidden secrets and characters. Slap Fight was also one of the earliest projects Toaplan made using game design documents, though Yuge claimed that these were added after development as postscripts, since the team "needed some written records".

Yuge stated that the weapon change mechanism was intended to be a strategic element in Slap Fight, as the player's ship is rendered invincible. The weapon power-up system was implemented early during the creation process, since the development team wanted to make "that kind of game", while each of the weapons' functionality and roles were decided to be good for certain sections in the title. All of the secrets were planned from the beginning of development and the team kept adding to the idea during the creation process such as secrets that required certain weapons. Another secret, the ship's satellite "option", was an idea suggested by Osamu "Lee" Ōta as a way to give the second player on a cocktail cabinet a purpose.

According to Tatsuya Uemura, not many arcade boards were produced for Slap Fight in Japan, but the game nonetheless proved to be popular among players. Japanese magazine Game Machine listed it as the seventh most successful table arcade unit of August 1986, outperforming titles such as Ikari Warriors and Gradius. Den of Geek noted its weapon system and multiple ways to kill enemies.

According to Masahiro Yuge, some of the ideas implemented in Slap Fight would later go on to influence development of Truxton. A spiritual successor, Grind Stormer (1993), uses a weapon power-up system reminiscent of Slap Fight. In more recent years, the rights to the game and many other IPs from Toaplan are now owned by Tatsujin, a company named after Truxton's Japanese title that was founded in 2017 by Yuge, and is part of Embracer Group since 2022.