Kurenai no Shinigami wa Nemurihime no Neoki ni Nayamasareru  

Princess Amaryllis, also known as Lily, of the Kingdom of Floit, is forced into a political marriage in order to forge an alliance with the Eras Empire. Her husband to be is the feared "Crimson Reaper," Crown Prince Gesald. He doesn't seem to trust Lily however and maintains a distant attitude towards her. Lily, on the other hand, has no intention of becoming a figurehead queen and boldly clashes with Gesald. But she actually has a huge secret...!
(Source: Manga Mirai)