Daiteikoku, literally translating as "big empire", is set as a space-themed epic novel and parody reminiscent of World War II. Players follow the colorful and extensive cast of characters---many of whom are inspired by figures in world history (in a style similar to a certain popular anime)---as they enact the major events which defined the World War II period alongside a slew of anime-style tropes, hijinks, and amorous interactions with the game's main protagonist.

As a full-fledged eroge, Daiteikoku features several erotic encounters between the protagonist, Tougou Tsuyoshi, and the game's female cast. (No yaoi or yuri scenes are depicted in this game.) Scenes are obtained by completing specific events and gameplay objectives. For those who wish to enjoy the game without viewing erotic content, all but a few brief occurences can be skipped simply by not selecting "H" events where available, which are clearly marked.