Update: thanks to Metal we found out this was a port of a Japanese PC game that was released on the NEC PC-9801 and Sharp X68000!
Imperial Force (インペリアルフォース) is a cancelled space-combat simulator / strategy adventure that was in development by SystemSoft around 1992 and it would have been published by Takeru (AKA Sur de Wave, mostly known for being the developers of Little Samson and Cocoron for the NES) for PC Engine. A short preview for the game was published in PC Engine Fan magazine (May 1992) and japanese collectors even found an early prototype of the game, that was sent to the gaming press at the time. In the end Imperial Force just vanished and we don’t know if this PC Engine port was ever completed before being canned.
If you can translate the most important details found in the japanese previews preserved in the gallery below, please let us know in the comments!