The release of a counter-virus, cultivated to destroy the virus' avian carriers in a desperate attempt to stop the spread of the disease, ends up backfiring as birds who resisted the counter-virus instead developed human-level intelligence.Society has adjusted to the avian conquest, though with minor bird-related cultural changes—for example, while some holidays such as Christmas and Tanabata are celebrated much as they are in the present day, a major event in the game is Legumentine's Day, an amalgamation of the traditions of Valentine's Day and Setsubun.In the 2014 remake however, the option to save is available at all times, the skip function is retained, and text is no longer highlighted.In both versions, the game's interface and controls change from that of a standard visual novel to similar to that of a '90s-era turn-based role-playing game during certain segments of the narrative.
Hatoful Boyfriend is an interactive text-based visual novel that follows a branching plot line, with the player's decisions determining which of the game's multiple endings they receive.
Pigeo Nation's Institute, an elite school for birds—as she finds love among her avian acquaintances.
Bad Boys Love, a hidden alternate story mode, opens with the discovery of the protagonist's corpse, after which the player follows her best friend Ryouta Kawara as he investigates the circumstances of her death and unravels darker conspiracies surrounding the school.
In a departure from the generally lighthearted romantic routes, Bad Boys Love is presented as a murder mystery psychological thriller, and is significantly longer than any other route in Hatoful Boyfriend, making up most of the game's actual length.
There are several changes to gameplay and the way text is displayed during Bad Boys Love in the original version of the game: saving is disabled except at certain points in the story, the function to skip dialogue and interactions is removed, and plot-important dialogue and narrative are highlighted with colored text; usually yellow, though text of particularly critical importance is highlighted in red.