Koukyuu no Kunkouhi

Xuan Xiang, the "Atonement Concubine," is imprisoned in the imperial harem due to the sins of her ancestors. One day, she finds the eunuch Hei Yao collapsed in front of her palace, a place rarely visited by anyone. After tending to him, Xuan Xiang asks for his help in obtaining the emperor's pardon and restoring her family's status. She is rejected outright, but Xuan Xiang deduces Hei Yao's "secret." Her basis? "Scent." Impressed by her extraordinary sense of smell, Hei Yao agrees to help.

The next day, Xuan Xiang suddenly becomes a candidate for Empress. This is Hei Yao's scheme, who claims that everything will be possible if she becomes Empress. However, a trial immediately arises. Xuan Xiang must identify scents in front of the four concubines, each a formidable competitor vying for the position of Empress...

(Source: Kadokawa, translated)