Thousands of years ago, Vampire King Akabara "Red Rose" Strauss lost both his kingdom and his queen. Since humans were unable to kill the queen, they sealed her away, erecting thousands of fake seals so that the king would never find her true location. Despite being pursued by relentless dhampires, Akabara continues to search for his queen to this day... Akabara's quest takes a sinister turn when an entity called the Black Swan appears. The Black Swan inhabits the body of a young human girl every 50 years, giving her the power to destroy the Vampire King and his queen. With each incarnation the Black Swan grows stronger--will the 49th Black Swan mean the end of Akabara?

From Kodansha:
When she was still just a girl, Kotoko was kidnapped by yokai. These spirits made her into a powerful intermediary between the spirit and human worlds, but this power came at a price: an eye and a leg. Now, years later, she watches out for dangerous yokai while developing feelings for a young man named Kuro, who is also special: an incident with a yokai has given him healing powers. He's surprised when Kotoko asks him to team up to handle renegade yokai, preserving the thin line between reality and the supernatural.

From: Easy Going Scans

Yoshino Takigawa is visiting his friend's family grave. After getting there, he encounters Evangeline Yamato, a woman in search for his friend, Mahiro Fuwa, who left a month ago to find his family's killer without any clues to who it might be. Evangeline informs Yoshino that two places where Mahiro has been spotted have been quarantined, due to an epidemic.

When Evangeline is questioning Yoshino at gun-point, Mahiro comes out of nowhere and swiftly saves him and can stop bullets in mid-air, claiming to have a deal with a sorceress; not just any, but the strongest sorceress, Hakaze Kusaribe, who promised to help find his family's killer with her magic so he can kill the killer himself.

After saving Yoshino, Mahiro informs him about the epidemic, a curse that turns living things into metal, claiming the Kusaribe clan plans to revive the Tree of Zetsuen that could destroy the world.

This is a spin off story that occurs about three years before Spiral. One of the main characters is Imari, who is in love with the kid who wants to be a detective, and which also quit school running after Kiyotaka, and it seems he's dating a murderer without knowing it...? But how is it all connected to the blade children? Not long after, our favorite blade children from Spiral appear for the rescue, all manipulated by Kiyotaka.