The world is in the midst of the industrial revolution when horrific creatures emerge from a mysterious virus, ripping through the flesh of humans to sate their never-ending appetite. The only way to kill these beings, known as Kabane, is by destroying their steel-coated hearts. However, if bitten by one of these monsters, the victim is doomed to a fate worse than death, as the fallen rise once more to join the ranks of their fellow undead. Only the most fortified of civilizations have survived this turmoil, as is the case with the island of Hinomoto, where mankind has created a massive wall to protect themselves from the endless hordes of Kabane. The only way into these giant fortresses is via heavily-armored trains, which are serviced and built by young men such as Ikoma. Having created a deadly weapon that he believes will easily pierce through the hearts of Kabane, Ikoma eagerly awaits the day when he will be able to fight using his new invention. Little does he know, however, that his chance will come much sooner than he expected...

Ever since her late mother took her to an aquarium when she was young, Tsukimi Kurashita has been obsessed with jellyfish, comparing their flowing tentacles to a princess's white dress. Now living with five other unemployed otaku women, 19-year-old Tsukimi spends her days as a social outcast dreaming of becoming an illustrator. However, her life changes forever when one day, a beautiful woman unexpectedly helps her save a jellyfish in a local pet store. From then on, the stranger—confident, fashionable, and the complete opposite of Tsukimi and her roommates—begins to regularly visit the girls' building. This trendy hipster, though appearing shallow at first, harbors some secrets of her own, starting with the fact that she isn't really a girl at all, but a wealthy male college student named Kuranosuke Koibuchi!

The world of psychology is far from strange to the unusual Dr. Ichirou Irabu, a resident psychiatrist of Irabu General Hospital. He and his charming nurse Mayumi run through several patients, each suffering from a mental illness that harms their everyday life. Patients should be wary of the seductive Mayumi, with her spellbinding looks and devilishly short pink nurse uniform. On the other hand, the doctor seems to have three separate personalities: a child with an oversized lab coat; an intelligent, youthful man with feminine traits; and a selfish, outgoing green bear. While curing his patients in questionable ways, Dr. Irabu often tries to gain something from them outside of his profession—and in doing so, occasionally forgets his role as a doctor. As each patient struggles to face the nature of their distress, an obvious yet invisible thread ties their paths together.

To the outside world, Hanabi Yasuraoka and Mugi Awaya are the perfect couple. But in reality, they just share the same secret pain: they are both in love with other people they cannot be with. Hanabi has loved her childhood friend and neighbor Narumi Kanai for as long as she can remember, so she is elated to discover that he is her new homeroom teacher. However, Narumi is soon noticed by the music teacher, Akane Minagawa, and a relationship begins to blossom between them, much to Hanabi's dismay. Mugi was tutored by Akane in middle school, and has been in love with her since then. Through a chance meeting in the hallway, he encounters Hanabi. As these two lonely souls spend more time together, they decide to use each other as a substitute for the one they truly love, sharing physical intimacy with one another in order to stave off their loneliness.