Plot wise, they don't have much in common (except for the presence of demons and deities and different realms), so this recommendation revolves more around the general vibe and aesthetic of these two dramas.
If you like how things look in Lost You Forever, from the outfits to the colour palette of the scenery to the special effects and props, Love Between Fairy and Devil might just be your cup of tea.

Although Ancient Detective is a lot shorter and of lower budget, it shares many similarities with Mysterious Lotus Casebook.
Both dramas have a dark and grim aesthetic, have good coreographies when it comes to martial arts and focus mainly on two friends that meet by chance and solve cases they stumble upon along the way.
Mystery, found family and secret pasts are the big three for both these titles.