For centuries, the Poison Masters have refined the art of killing. Among them, the Gero clan is one of the five most influential Master families, boasting unmatched skill and influence. Hikaru Gero, the heir to this infamous lineage, has spent his entire life hidden in the underworld's shadows, far removed from love or marriage.
However, to ensure the Poison Master bloodline continues, the head of the Gero family decrees that Hikaru's sister must bear an heir. Soon after, Hikaru encounters Mei Kinosaki, a brilliant marriage swindler who also happens to be his current assassination target. Determined to protect his sister and solve the succession issue himself, Hikaru makes an unexpected proposal on the spot—asking Mei to help him get married.
"...That's the first time anyone's ever proposed like that."
And so, with the cunning marriage swindler Mei as his advisor, the elite assassin Hikaru embarks on the toughest mission for love. His objective? The ultimate marriage. The most unlikely duo—an assassin and a marriage swindler—take on the world's toughest mission for love!