Hotel Del Luna (2019)

They both have reincarnation of characters. Lots of flashbacks and stuff. They both have a mystery vibe.

Both dramas contain references to the moon, and Yeo Jin Goo stars in both dramas (the ML in Hotel Del Luna and the younger version of Kim Soo Hyun in Moon Embracing the Sun).

Both are high fantasy genre Korean dramas written by Hong Sisters. Hotel Del Luna is modern, AoS is historical fantasy. FLs are used to be assassins before.

the actors look very similar lol. you should definitely give hotel del luna a watch. there are small resemblances here and there.

both have "things not everyone can see" vibe going on, as in the hotel with the ghosts for Hotel Del Luna and the realization of the life outside the comic in Extraordinary You
the link to the past ("past" in EY case being previous story)

and similar ending

Both are set in a hotel.
Both have a scene of mystery and suspense.
(SPOILER) Both have a romance that slowly blossoms over time.

recommendations are not just about similarities, so I'll just say (beside be melodramatic) TTON is the drama that got me out of my HDL slump~