Bride to the Lord of the Underworld

Kikuka is a server at Hananoya, a high-class restaurant frequented by well-to-do politicians and entrepreneurs. She's also the daughter of the establishment's current owner and his late mistress. Her mother was kind and gentle, but suffered from illness, and eventually passed on to the next world. Since then, Kikuka has been working hard at Hananoya while enduring constant mistreatment from her mother- and sister-in-law. She never argues back, keeping her promise to her mother: always smile and never resent those around her. But when her sister-in-law grows tired of putting up with her, she's abandoned in the mountains one night. However, before despair takes ahold of her, Kikuka stumbles upon the rumored pavilion, Hell's Gateway. There, she meets Homura, a man with glistening, vermillion hair and otherworldly beauty... And for reasons she cannot understand, he treats her with a warm kindness that she's never known...

(Source: Manga Plaza, translated)