The player needs to keep his relationship up with all the potential suitors.
If one falls too low, then the suitor gains a "bomb." When the suitor has a bomb, then she'll gossip about the player to the other characters, lowering his relationship with them.
The game plays with the expectations of genres: aside from the obvious change in expectations (you date birds), the game is very self-referential and plays with tropes inherent in video games.
Hatoful Boyfriend shifts into a fighting style game during one potential suitor's route, and the second half of the full version turns into a dark, espionage thriller.
Despite Western thought, dating sims are not necessarily pornographic.
Popularized by a Let's Play on the website Quarter to Three, Hatoful Boyfriend took the Internet by storm, as shown by a massive amount of fanart and fanblogs on sites such as Tumblr and Pixiv, and helped bring dating sims back into the public consciousness.
A higher social rank also means that characters will give each other better benefits (higher dodge rate and higher attack skill, for example), with the S rank as the highest.
Through cut-scenes, their relationships improve as the characters climb up ranks, culminating in S rank, which is only unlockable with two characters of the opposite sex and which enables them to marry.
The adult games page is easily more popular, with some games reaching views in the millions.
With titles such as "Aching Dreams2 Hentai Game," "Meet'N'Fuck Road Trip," and "Orgasm Girl," it's pretty obvious what sort of direction these games are heading into.