Ryuujin-sama no Futago no Tsugai

Tsubomi, a member of a minor branch of the Asagiri family, is treated as an outsider by her family, especially in comparison to her favored younger sister Saki. Her life changes when she encounters Homare, the future leader of the Asagiri family. When their hands touch, a glowing "Dragon Seal" appears, and Homare announces his intention to take her as his bride. However, due to the influence and schemes of their families, Saki also becomes a bride candidate and moves into the main household.