Brought up in a conflict-ridden environment, child soldier Jonathan Jonah Mar hates weapons and those who deal them. But when Koko Hekmatyar, an international arms dealer, takes on Jonah as one of her bodyguards, he has little choice but to take up arms. Along with Koko's other bodyguards, composed mostly of former special-ops soldiers, Jonah is now tasked with protecting Koko and her overly idealistic goal of world peace from the countless dangers that come from her line of work. Jormungand follows Koko, Jonah, and the rest of crew as they travel the world selling weapons under the international shipping company HCLI. As Koko's work is illegal under international law, she is forced to constantly sidestep both local and international authorities while doing business with armies, private militaries, and militias. With the CIA always hot on her trail, and assassins around every corner, Jonah and the crew must guard Koko and her dream of world peace with their lives or die trying.

Kou Ichinomiya is the son of a wealthy businessman who holds a firm belief in his elite status. As such, he is determined to avoid becoming indebted to anyone; but one day, after a run-in with some mischievous kids on Arakawa Bridge, he ends up falling into the river running underneath. Luckily for him, a passerby is there to save him—but now, he owes his life to this stranger! Angered by this, Kou insists on paying her back, but this may just be the worst deal the arrogant businessman has ever made. The stranger—a stoic, tracksuit-wearing homeless girl known only as Nino—lives in a cardboard box under the bridge and wants only one thing: to fall in love. Asking Kou to be her boyfriend, he has no choice but to accept, forcing him to move out of his comfortable home and start a new life under the bridge!

Yukito Kunisaki is on a journey in search of the Winged Maiden who was bound to the sky centuries ago, after hearing an old childhood tale from his mother. As Yukito shows his puppet show to people in an attempt to make some money, he finds himself in a small town in which he did not expect to stay very long. However, when he meets an unusual girl named Misuzu, things take a drastic turn as he is invited to stay with her. By staying in the quaint town, Yukito soon becomes friends with the locals. As he gets to know them better, he learns of their problems and decides to help, putting his search for the Winged Maiden on hold. With his search on hold, and his growing attachment to Misuzu and the small town, will Yukito ever find the Winged Maiden, or is she closer than he thought?

The once-feared Demon Lord Satan of Ente Isla, who had to flee to Earth after being defeated by the hero Emilia Justinia, is now leading a peaceful life in Tokyo under the alias Sadao Maou. Having become a model employee of a local fast-food restaurant, Sadao has to provide for his former generals Alciel and Lucifer who joined him in Japan, as well as avoid confrontations with Emi Yusa—the assumed name of Emilia—and the angels who monitor his actions. Amidst a violent argument between Sadao and Emi, a dimensional portal suddenly appears, carrying a mysterious apple that harbors a toddler named Alas Ramus. To everyone's bewilderment, she imprints on Emi and Sadao, marking them as her parents! After Emi reluctantly agrees to help Sadao take care of Alas Ramus, their semblance of normal life is jeopardized by the appearance of the archangel Gabriel, who comes bearing bad news. He claims that he must take both Alas Ramus and Emi's sacred sword with him—lest the world be destroyed. Unable to accept Gabriel's grim prophecies, the hero and the former Demon Lord need to put their differences aside and unite to protect what they hold dearest.