All of a sudden, they arrived: parasitic aliens that descended upon Earth and quickly infiltrated humanity by burrowing into the brains of vulnerable targets. These insatiable beings acquire full control of their host and are able to morph into a variety of forms in order to feed on unsuspecting prey. Sixteen-year-old high school student Shinichi Izumi falls victim to one of these parasites, but it fails to take over his brain, ending up in his right hand instead. Unable to relocate, the parasite, now named Migi, has no choice but to rely on Shinichi in order to stay alive. Thus, the pair is forced into an uneasy coexistence and must defend themselves from hostile parasites that hope to eradicate this new threat to their species. [Written by MAL Rewrite]

Shun Asanaga is a 15-year-old junior high school student with an optimistic and bright personality. One day, he finds a mysterious crystal in the office of his father, who is a scientist and businessman. When Shun touches it, the world becomes distorted, and he is sent into the world of Endra. Emilio, a prince of the kingdom of Endra, is nearing his 16th birthday and despises the reigning king, Delzain. Since Emilio is now at the age when he can inherit the throne, he takes up a weapon and attempts revenge. However, because Emilio is too weak, he is captured by Delzain and put in prison. When Emilio is in grief, the wall of his cell becomes distorted and Shun appears from there with two goals: return to his own world, and complete Emilio's revenge. What future lies ahead for the two boys trying to survive in Endra, yet raised in two different worlds? (Source: MAL News)

In a world of magic and monsters, Krylancelo Finrandi and his foster sister Azalie Cait-Sith were once promising students of sorcery, prodigies at the famous Tower of Fangs. But an experiment gone horribly wrong warps Azalie's appearance, trapping her in the form of a dragon. Elders at the Tower—more interested in preserving their reputation rather than their students' lives—drive off the transformed Azalie and cover up the incident. Outraged, Krylancelo strikes out on his own, taking the new name of "Orphen" and vowing to return Azalie to her normal state. Five years later, Orphen's quest has stalled. A chance encounter brings him face to face with Azalie again, but he still has no way to restore her body. And with a hostile group of sorcerers hunting her down, he may be running out of time. The past and present collide as Orphen tries to find how to save Azalie from their former teachers and friends. [Written by MAL Rewrite]

The story takes place in Japan. The year is 2030 and Earth has been completely overrun by a viral disease named "Gibia" that turns infected people into various different monsters, based on their age, sex, and race. A samurai and a ninja from the early Edo period travel together through time and arrive in a ruined Japan to aid a professor working on a cure for the virus. Together, they fight countless Gibia monsters, outlaws, and other fierce foes on their journey to save mankind.