Botsuraku Reijou desu ga, Kono Tabi Tsundere Kishi-sama no Koibitoyaku ni Narimashita

"Who would ever worry about you?!" Rimmel used to be a noble, but after her family lost everything, she now lives as a commoner and works at a bar. Her childhood friend Hewitt, the heir to the Count Stan family, often visits, but only to make sarcastic comments. Ever since Hewitt declared he wanted to become a knight at age twelve, they've grown apart. Rimmel thinks Hewitt is coming to the bar just to see Heather, the baron's daughter who helps run the bar and is popular with the customers. One day, Rimel spots the swindler who ruined her family's life.She asks Hewitt for help, but the man escapes. Later, the knights ask Rimmel to help with their investigation, by pretending to be Hewitt's lover to lure the criminal out. Now, caught up in something much bigger than she expected, Rimmel must face the past she tried to leave behind.

(Source: Shusuisha)