Kurenai no Shinigami wa Nemurihime no Neoki ni Nayamasareru

Princess Lilith of the Kingdom of Freud in Amaryllis, is to have a political marriage for an alliance with the Empire of Ayrras. Her husband to be is Crown Prince Gesualdo, who is feared as the "Crimson Reaper." Gesualdo does not trust Lilith and maintains a cold attitude towards her. Not discouraged, Lilith has no intention of remaining a decorative princess and boldly confronts Gesualdo. However, Lilith actually has a secret...!

(Source: Shufu to Seikatsu-sha, translated)