Recommendations

In terms of story they are slightly different but are similar as to the relationship dynamics between the main couples and the psychological vibes. Both can be classified as romance that at some points have unsettling events happen between the couples.

1. There was Romance and that was a happy ending; a bittersweet one!
2. Not a shortage of tragedy events; be warn this is a war movie.
3. Very family oriented; this is the most heart breaking part of the series.
4. Based on actual historical events.

Started off with a fake marriage. FL marries in order to find out the murder of her father. She purposely gets close to the ML to get closer the his boss.

in both:
*FL is famous celebrity
*ML becomes bodyguard
*love/hate relationship

A love to kill is much better also dark drama.
If you liked this things in Nang Rai Tee Rak you can try this Kdrama.
Though I'm not sure if after "love to kill" it's proper recommendation (these dramas are on different level).

Both movies evolve between The young man and the old man relationship. The care free spirit of young man vs the discipline knowledgeable stubborn old man. Sweet and heart warming movies

Both movie involve man with big muscle. Both main lead had been through up and down, hard training, big strong man with sweet soft heart.

Both movies about the main male lead were not happy in the big city. At the beginning was reluctant to go to the country side. The under privilege children ended up was the driving force to attract the teacher. Really good and heartwarming movies. Must watch

Althought one is music the other one is sport related, both main male lead have a loving soft heart for the under privilege children. It is amazing they bond together both good time and bad time

Similarity,
1) Older Woman/Younger Man
2) Smart and Successful female lead
3) My Favorite ( Song Hye Kyo )
4) Nice and Smart Male lead
5) Photography
6) Melodrama

Just like Sky Castle, in Melancholia, parents - rich parents are involved in lobbying for their kids to get admission in high universities by pressuring them to study under strict schedule, special classes and take extra courses.

And just like SC, poor are also trying their best to get in line, but are treated poorly and the genius children of poor class, suffers at the hand of school injustice, corruption and is belittle and looked down upon by rich kids.

Both movies depict the love stories of a couple where one person has dementia and their significant others don't.

They are super similar with the main difference being in one movie the FL has dementia and in the other the ML has dementia.

The young woman in foreign country met the love of her life. Learning new skill. Attempting to survive without loosing her dream

Heart warming story. War is sad. Children and youngsters together attempt to live and survive. The teachers rescue them.

The young man and elderly lady relationship growth. Found out so much heartwarming story about the old lady. The old lady have whole life full of roller coaster experience. Sweet movie.

The relationship between the young man and the elderly develop nicely. The old has deep story to tell. Whole life full of experience and knowledge. They became coexisting family.