Shiyounin Reijou no Junan: Kioku Soushitsu no Konyakusha to Nidome no Koi

Lisary falls in love with Marquis Orion's only son, Hugo, while working as a servant in the Orion manor. Many protest the idea of a nobleman marrying a servant, but through the power of their love, Lisary and Hugo convince the marquis to allow their marriage on the condition that she go away to finishing school to learn how to be a proper aristocratic bride. Though both their hearts ache to be separated, she departs for the school... Six months later, she returns from her studies and rushes straight to Hugo's side. However, her excitement at finally seeing him again is cut short when he looks at her and blearily asks, "Who... are you...?" Thus begins a fantasy romance about this former count's daughter, raised as a commoner, and her second chance at love with the amnesiac nobleman her heart desires! (Source: Manga Plaza)