In 19th century Paris, Claude Claudel and his grandfather Oscar run a metalworking shop tucked away in the Galerie du Roy shopping arcade. Back home from his recent travels, Oscar appears with a young Japanese girl—Yune—by his side. Although he is initially against it, Claude comes to accept Oscar's announcement that Yune will live and work with them going forward. Bewildered by Yune's foreign customs, Claude must balance looking after her and managing the shop. But over time, as she settles into her new role as a live-in maid, Claude slowly shows interest in learning to understand Yune and the vastly different world she comes from.

While the perfect getaway for most girls her age might be a fancy vacation with their loved ones, Rin Shima's ideal way of spending her days off is camping alone at the base of Mount Fuji. From pitching her tent to gathering firewood, she has always done everything by herself, and has no plans of leaving her little solitary world. However, what starts off as one of Rin's usual camping sessions somehow ends up as a surprise get-together for two when the lost Nadeshiko Kagamihara is forced to take refuge at her campsite. Originally intending to see the picturesque view of Mount Fuji for herself, Nadeshiko's plans are disrupted when she ends up falling asleep partway to her destination. Alone and with no other choice, she seeks help from the only other person nearby. Despite their hasty introductions, the two girls nevertheless enjoy the chilly night together, eating ramen and conversing while the campfire keeps them warm. And even after Nadeshiko's sister finally picks her up later that night, both girls silently ponder the possibility of another camping trip together.

Mysterious immortal humans known as Ajin first appeared 17 years ago in Africa. Upon their discovery, they were labeled as a threat to mankind, as they might use their powers for evil and were incapable of being destroyed. Since then, whenever an Ajin is found within society, they are to be arrested and taken into custody immediately. Studying hard to become a doctor, Kei Nagai is a high schooler who knows very little about Ajin, only having seen them appear in the news every now and then. Students are taught that these creatures are not considered to be human, but Kei doesn't pay much attention in class. As a result, his perilously little grasp on this subject proves to be completely irrelevant when he survives an accident that was supposed to claim his life, signaling his rebirth as an Ajin and the start of his days of torment. However, as he finds himself alone on the run from the entire world, Kei soon realizes that more of his species may be a lot closer than he thinks.

Hotaru Tachibana has a strong sense of justice and just cannot help confronting those who choose to perform malicious acts. Furthermore, Hotaru is actually a girl who likes to disguise herself as a boy. After hearing rumors that her best friend was tricked by the popular host of a local club, Hotaru seeks to punish the evildoer. Upon arriving at the club, however, she is challenged to a so-called survival game by the host Masamune Matsuoka, where the first person hit by the bullet of a toy gun will lose. After a destructive fight which results in Hotaru's loss, Masamune forces the young boy to join his survival game team named Toy Gun Gun, in order to repay the cost of the damages that he has caused inside the club. Although she is initially unhappy with this turn of events, Hotaru quickly begins to enjoy what survival games have to offer and is determined to pay off her debt, much to the dismay of Tooru Yukimura, the other member of Toy Gun Gun. As time goes on, Hotaru begins to develop a close friendship with the rest of the team and hopes to take part in realizing their dream of winning the Top Combat Game (TCG), a tournament to decide the best survival game team in Japan. Although Hotaru tries her best, there are just two little problems: she is absolutely terrible at the game, and Toy Gun Gun doesn't allow female members on their team!