Mujikaku Tensai Renkinjutsushi no Henkyou Machizukuri: Boujakubujin na Ane no Kawari ni Hatarakasarete Ita Imouto, Henkyou Ryouchi ni Sasensareta to Omottara Matte Ita no wa Ouji-sama Deshita!?

Lumina has faithfully served as an alchemist at the royal court, shouldering responsibilities that rightfully belonged to her frivolous older sister. Abandoned by her family and neglected by her fiancé, she endures her isolation in silence. Her world is upended when her sister and fiancé abruptly annul their engagement and announce her transfer to a remote frontier territory. Resigned to losing both her status and her betrothed, Lumina travels to her new post expecting desolation, only to discover that Prince Elms of the Ratman Kingdom is waiting there to welcome her.