Firefly Wedding, Vol. 1

Satoko, the daughter of a Meiji-era nobleman, has a heart condition and little time left. Before she dies she wants to secure a marriage that will restore her worth in her family's eyes. Instead she becomes the target of Shinpei, a mysterious assassin. In a desperate attempt to save her life she proposes to him.

The proposal is not sincere, but Shinpei loves as intensely as he kills, and he takes "until death do we part" literally. Satoko must now find a way out of the engagement without losing her life. A dark shojo romance with a dangerous love interest.