The cast of characters is indeed composed entirely of seductively gorgeous pigeons.
A self-described “heartwarming love story” – it is a parody of a female’s dating simulator with an English title of “Hatoful Boyfriend”, a genre of game typically consisting of a female main character of the human race and many males (also human). The female, as controlled by the player who is also coincidentally female in most cases, makes a series of decisions brought up during conversations and situations so he can achieve a “happy ending” with one of the male bird characters.
That is still the case with this game, except the females are pigeons. It is difficult to understand what exactly this is all about – although according to the game’s official site, a female enters the classroom of a prestigious school on the first day only to find the room full of pigeons. The story then continues as this girl decides “a bird is fine too” and learns of the soft, tender side of birds she’s never noticed before.
The player takes the role of that pigeon fetished freak female human who interacts with the male pigeon students of the school, no different than any harem love story.
Originally, the creators intended for it to be an April fools joke, although as development went on beyond April first, it became simply the best pigeon dating simulator on the market and they wanted to take advantage of that. Released in Akihabara on the 25th, it sold out immediately the same day.