Firefly Wedding, Volume 1

Afflicted with a heart condition, Meiji-era noblewoman Satoko is determined to secure a marriage that will benefit her family before she dies. But before she can realize her goal, she's targeted by a mysterious assassin named Shinpei. In a last-ditch effort to save her life, Satoko asks her would-be murderer to marry her. Her proposal isn't sincere, but unfortunately for her, Shinpei loves as intensely as he kills. Can Satoko find a way to break the engagement without losing her life?