Until We Meet Again (2019)

While in itself being quite different ( Mermaid mystery vs. BL drama) they both share a plot of reincarnation and rediscovering the past memories and the hidden conspiracies around their past selves. I really love both of them a lot and rewatched them several times. If you are looking for something fresh and fluffy, check them out!

Both are LGBT dramas with heavy reference to the Red Thread myth of fate (I honestly wish more dramas had plots with this)
Apart from the obvious difference that YMMD is a kdrama and UWMA is a Thai drama, YMMD is kinda lighthearted and short, while UWMA starts with a dark undertone (don't worry, it gets fluffy later) and is longer.
Besides that, UWMA is a must watch for BL fans - I can't help but gush over it!

The red string fate... Always been a huge fan of this concept... Though both the dramas depict it in a different way... But who wouldn't love the coincidences of fate...

Tragical stories of not acceptance...where at the end hidden unrequited love is the strongest hope to give life second chances for keep loving...

They are from the same Studio and have the same director <3
The story isn't similar
But both have great chemistry and they are a really cute couple!
I really loved this serie!

If you are drawn to the premise of red string of destiny and reincarnation, then Until We Meet Again and Tomorrow do have something in common, even though both are shows from different genres. Both shows are dealing with suicide, destiny and reincarnation, also showing flashes of past lives as memories or dreams, but have different approach to showing how suicide affects the connections with the loved one's in the next lives.

These dramas have very different setting (thai university - UWMA; office - ChM) but give off overall similar vibe:

Both are BL dramas with shy main lead and confident/perfect love interest who cares a lot about him.
The romance both dramas portray is very soft and cute.
Both dramas have fantasy element (reincarnation - UWMA; mind reading - ChM) and cute side-couple.

In both series, love spans time. There is a feeling of 'I will always love you' even if the circumstances that brought us together may also keep us apart. The love in both is ethereal and unwavering.

Both drama's main theme are reincarnation and romance......................................................

Very similar theme: a soulmate type of BL that has a very turbulent journey before finally reaching happiness. Definitely a most watch.

Both dramas are BL genre that takes place in campus setting. The families of the male leads in both dramas feature prominently and affect the relationship of the male leads.