For centuries, the Poison Masters have perfected the art of assassination. Among them, the Gero family stands as one of the five most powerful families of Masters, wielding unmatched skill and influence. Hikaru Gero, heir to this infamous bloodline, has lived his life deep in the shadows of the underworld, far removed from love or marriage. However, to ensure the Poison Master bloodline does not die out, the head of the Gero family declares that Hikaru's sister will be forced to bear an heir. Soon after, Hikaru crosses paths with Mei Kinosaki, a brilliant marriage swindler who also happens to be his current assassination target. Determined to protect his sister and solve the succession problem himself, Hikaru makes an unexpected request 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 sets out on the toughest mission for love. His goal? The ultimate marriage. The most unlikely duo—an assassin and a marriage swindler—take on the world's toughest mission for love! (Source: Official site)

In an isolated village, two twins were born, separated by day and night. It is years later, and while the older brother Yuru has become a hunter of animals, his sister Asa has been locked away in a cage, ordered to perform a special duty that prohibits her from meeting more than a few select individuals. On an otherwise inconspicuous day, a group of armed men riding in helicopters, referred to as dragons by the citizens, assaults the village in search of Yuru, killing every adult on sight. When Yuru attempts to meet up with Asa and flee, he finds a dead body instead—on top of that, the person who killed her claims to be Yuru's true twin sister. Before the woman can capture him, Yuru is rescued by a man named Ryuu Dera Tadera, an outsider who frequently visits the village. However, it is not long before the two are cornered. In a last-ditch effort, Dera makes Yuru give a gift to the deity of the village, summoning a pair of daemons whose existence is bound to reveal the truth behind these chaotic events.

TV Special adapting chapter 431 included in the final volume of the manga.

Second season of Vigilante: Boku no Hero Academia Illegals.