Daiva 6: Imperial of Nirsartia is the sixth in a series of seven Daiva games that were all released simultaneously on different platforms. Most of the other versions ended up on Japanese computers such as the PC88, PC98 or MSX. The series is not a collection of sequential stories, but rather a presentation of the same story from the perspectives of seven different protagonists. There was also a separate comic book and other media released around the same time as part of a huge media blitz to promote the games, all based around the galactic civilization Daiva.
All of the Daiva games were developed by T&E Soft, who were perhaps best known at the time for the Hydlide series of action RPGs. Daiva 6 was published by the music giant Toshiba-EMI.
The player must explore the planetary systems and take over enemy locations, all the while protecting their own, like in Star Raiders. A big difference, however, is that the player is expected to take over planets manually by dropping down to the planet in a mech. The player can call on three types of support: Missiles, which home-in and eliminate random enemies; bombs, which clear the screen; and a refill item which recovers the player mech's health. The player chooses where to drop these power-ups at which points during the level before actually entering it, thereby requiring some degree of strategic preparation before the assault.
The action stages are all side-scrolling shoot-em-up action levels reminiscent of something like Side Arms or Thexder. The goal is to simply make it to the other end of the stage without losing all the mech's shields and being destroyed. Each stage has a different amount of gravity: On most stages, the mech drops to the bottom and the player can apply a little thrust to make the mech glide and jump over enemies and obstacles. Occasionally, the gravity is so great that the mech is very limited in its vertical movement.
In addition, the game also has strategy elements. It has strategic turn-based battles whenever the player's mothership encounters other spaceships in deep space. The player selects where they want to move/fire and the turn plays out. Though primitive, Daiva 6 has one of the earliest examples of the TBS genre, which would eventually become very popular on the Famicom and other Japanese computers.