"Get married and I kill you." This was the letter sent to Kimihito, an ordinary guy living with a houseful of extraordinary beauties, by a mysterious writer known only as "D." Now it's up to Interspecies Coordinator Smith, Kimihito, and his ever-increasing menagerie of monster girls to find out who is behind the threatening letter before it's too late. The game plan? Use Kimihito as bait by sending him on a series of dates with monster girls. Along the way, several possible suspects emerge, each of whom has a "D" connection of one kind or another. Meanwhile, Kimihito's potential brides each begin acting strangely. Are they taking the fake dates too seriously—or is something (or someone) fare more sinister at work?