Bulgasal: Suflete nemuritoare (2021)

Será que depois que morremos tudo acaba ou apenas é o começo? Esses dois dramas abordam reencarnação e expiação dos pecados de uma forma bem envolvente, você vai encontrar também bastante suspense e ação, as histórias são complexas ,vidas são entrelaçadas e problemas e segredos são desenterrados , garanto que irá te entreter afinal são ótimos shows.

I don't know how to explain it right, but both of these fantasy dramas gave me a certain vibe that makes me believe that if you liked one of them, you would like the other as well.
Now, if you haven't seen any of these dramas and you don't know where to begin I could just simply say (without spoilers) that "the gu family book" has more "clear" romantic moments.

The series tells The story of a man-turned-immortal, Bulgasal, who wants revenge from a woman with a mysterious past and present, who he deems responsible for his immortality and miseries from the past 600 years, hoping to free himself from his curse.

Episodic saga from the first half of the 20th century follows Hero Hua from an ill-omened June day in his youth to a showdown 17 years later with a disaffected member of his martial-arts school, a Japanese named Invincible. Tensions between Chinese and Japanese, plus U.S. racism, mark the tale. Hero marries Jade, leaves her in China when he goes to America as an indentured servant, rebels against cruel labor conditions, and is joined by her in New York City where she has twins. Jump ahead 16 years: their son Sword comes to New York looking for his father. There, Sword hears many stories of his father, which we see in flashbacks, and the stage is set for the battle with Invincible.

Kariya Yuri is an airhead who falls head-over-heels in love with Aono Ryuhei after their very first meeting. Yuri's happiness knows no bounds when Aono surprisingly ends up agreeing to go out with her, and thus she starts to enjoy her perfect relationship with her perfect boyfriend. Alas, misfortune strikes when only two weeks into their relationship, Aono tragically dies in an accident. But is something as simple as death really enough to keep the two lovers apart?

Tatsuya was killed in a car accident and his spirit lives in Hikata - the one who killed him in the accident. Since then, he had a hard time trying to change his girlfriend's perception of "him" or "Hikata" while still trying to protect her.

Seon Woo receives calla every morning and wants to find out who the secret admirer is. One day, he goes to a nearby florist’s where he meets Ji Hee. He falls in love with her at first sight, thinking she is the one who is sending him flowers. Seon Woo asks Ji Hee to go on a date, and she agrees. He arrives at the rendezvous only to find that Ji Hee is held hostage and, to his horror, killed before his eyes.

Cha Seung Hyo is an abandoned child who gets adopted in the United States and grows up to be a cold hearted person. Son Il Gun is a father who died, but he left things unfinished with his daughter. In order to make sure that his daughter is provided for he controls Seung Hyo's body for three hours a day for 49 days. He buys his daughter the things he couldn't do when he was alive with Seung Hyo's money. Il Gun's daughter, Young In, is a quick-tempered girl who meets Seung Hyo during her part-time job. At first she has a bad impression of him but she gradually starts to fall for the lonely Seung Hyo who is unable to open up to anyone else because of his bitter past.

Korean potter Jun Ho meets successful young entrepreneur Nanami in Tokyo. The couple falls in love and soon marry. A year after their marriage, tragedy strikes when Nanami is killed on her way home. Nanami, not ready to leave this world, remains in this world in spirit form. During this time she learns that her death wasn't an accident and her husband Jun Ho is in imminent danger. Unable to contact any humans except a psychic named Unten, can Nanami warn Jun Ho before harm comes his way?

Both are supernatural dramas with vampire/vampire-like creatures. The protagonist in both dramas transforms into a monster after a traumatic experience. They both also refuse to turn completely into a monster and stay partly human.

The same atmosphere
Dark
Characters with monstrous strength
Violence and gore but it's more extreme in Bulgasal than L.U.C.A

-(Bulgasal)-
Deals with immortal beings and the humans their fate are tied to throughout many reincarnations.
Tragic pasts, how to resolve it and trying to protect those you love.

-(Tommorrow)-
A team of grim reapers from previous lives that chose the job.
This special team helps to prevent those wishing to commit suicide by helping them realize they want to live and why.
Also deals with fate and the strings that connect people through their reincarnations

Rebirth story, Male and Female lead were past lovers (sort of).. Female lead who doesn't remember her past life when the climax of the show entirely depends on it..., slowburn romance, found family trope.. hunting monsters to protect the Fl, Male lead yearing to leave his monstrous existence and hopes to become a human....the similarities are endlessly)

In both series the male lead suffer from a curse and the key to lifting the curse lies with the female lead and in process the romance between them

Not necessarily related but lovers of one show might enjoy both.
Both have that sci fi element mixed with fantasy and monsters.