The Holy Grail of Eris, Vol. 1 (manga)

Connie is a viscount’s daughter with little notable attributes besides her sincerity, so when she’s suddenly framed for a crime she didn’t commit, it seems like the end of the line for her-until the ghost of Scarlet Castiel, an infamous villainess who was executed ten years ago, swoops in and clears her name. In exchange, Connie resolves to solve the mystery behind Scarlet’s untimely death…and in the process, uncovers a conspiracy that still haunts the present!