Another variation on the ‘fiancée stolen by a baron’s daughter’ setup, Akuyaku Reijou to Akuyaku Reisoku ga, Deatte Koi ni Ochita nara (massive subtitle omitted) features a nice mix of romance, comedy, and mystery. I’m not sure why the love interest is referred to as a villain though and the prince’s actions come across as exceptionally erratic. Unless he turns out to be a changeling (lot of talk about changelings) I could definitely see some major issues arising from that down the line.
A great deal of plot progression occurs in the seventh Kasei Madoushi no Isekai Seikatsu novel, with the protagonist being forced into coming clean about her origins and Alec resolving to re-join the royal family. Really, at this point all that’s left is to hold the wedding.