Trying to find the name/author of a book I've read a while ago. As far as I recall, this was a single book published in the late 80s (maybe 1987). Published in English. I want to say the cover had a white border with a picture of a space ship/battle cruiser inset within the border, but this detail is not reliable. I've looked at sources (Wikipedia, Goodreads) for books published around this timeframe, but they either didn't provide enough detail for me to connect the dots or didn't seem to be what I was remembering.
Setting is in space with a civilization/empire known for its militaristic conquest. The protagonist is an alien/cosmic entity who possesses the body of a ruthless/brutal commander just prior to his armada engaging an enemy in battle. I believe the entity refers to it as a "game" they play from time to time.
During this initial battle the entity/commander asks the chief engineer to develop a new weapon to turn the tide for them. I believe it was a space mine of some sort. As a result of the battle, a daughter of the opposing commander is taken as a companion to the entity (IIRC, to ensure no further hostilities). She stays with him throughout the story. The new weapon/space mines make an appearance later in the story as well.