International Assassins arc

Running from chapter 53 to chapter 70, the arc takes over from the Bomb Girl story and sets up the Gun Devil arc. It floods the cast with hired killers, chief among them Quanxi with her harem of fiends and the doll-summoning Santa Claus, and builds toward one of the saga's bloodiest battles, fought inside Hell itself.

As Denji's televised wins make him a celebrity, Makima warns that assassins from around the globe are closing in on Japan to take his heart. She assigns a rotating guard of devil hunters and insists everyone's strength will be needed against the Gun Devil the next year. Contracts go out worldwide: three immortal American brothers, the Soviet pair of Master and Tolka, China's lethal fiend-hunter Quanxi with her four lovers, and Germany's Santa Claus, who demands children for contracts as her fee. Posted beside a lake under heavy watch, Denji serves as live bait. The American brothers strike first, killing Kurose and Subaru, after which the eldest borrows a Skin Devil contract to wear Kurose's face and slip into the group. Power sees through it and runs the imposter over with Kobeni's stolen car, and Yoshida later executes a second brother, sparing only the queasy Aldo. At a burger shop, Master discreetly drives a cursed nail into Denji, advancing Tolka's killing assignment.

Santa Claus opens her offensive by turning civilians into a doll army that herds the hunters into a mall, where Kusakabe's Stone Devil holds the line. Quanxi then arrives and scythes through hunters and dolls alike, downing Yoshida and trading blows with Kishibe, who proposes an alliance to kill Makima. The mayhem builds until Santa Claus invokes a Hell Devil contract to drag everyone present into Hell. There the survivors forge an uneasy truce, only to meet the primal Darkness Devil, which lops off hands, decapitates Tolka, and slays Quanxi, Beam, Tamaoki, and more with ease. Makima has Princi teleport her in, and by wielding Tolka's body she forces the Hell Devil to return everyone to the living world, taking a grievous wound herself.

Back on the surface, Makima revives Denji, who battles Santa Claus and her growing horde, even dousing himself in gasoline and igniting to ruin her body. Tsugihagi triggers Quanxi's shift into her Bow Hybrid form, and the two shred the dolls before Santa Claus turns more of Quanxi's lovers against her. In the end Quanxi has Cosmo bury Santa Claus's mind beneath an endless Halloween crammed with all the universe's knowledge. Makima then beheads Quanxi and her girlfriends as the blindfolded Kishibe and Yoshida look away. A reporter notes survivors left able to utter only the word Halloween, with Aldo melting into the crowd. Newcomers across the arc include Quanxi and her fiends Cosmo, Long, Pingtsi, and Tsugihagi, the assassins Master and Tolka, Germany's Santa Claus, the American brothers Aldo and Joey with their eldest sibling, the hunters Kusakabe, Tamaoki, Yoshida, Subaru, Tomono, Sato, and Nakamura, plus the Stone, Doll, Octopus, Grape, Darkness, and Hell Devils.