Black

Similar in atmosphere story and chemistry.
About the relationship, both are incompatible entities that work together to save people and solve mysteries.
Wonderful teamwork.
Both are horror comedies.

Similar in - relationship, more like a vibe of the romance, the ending has similar under the theme, both ML are somewhat different in kind from the FL, FL's are strong and grow. Overall it gave me the same feeling watching both.

Grim Reaper falls in love with a human who can see them, love interest has a past history with reapers, in order to correct past mistakes, making choice to banished from all existence or never existing.

In both shows the Male Lead pretends to be someone they are not in order to use the Female Lead. However, they end up falling in love with her and, in so doing, they betray their original mission in favor of keeping her safe.

Both a supernatural romance..One woman can see the future in her dreams the other can see how someone dies by touching the black shadow that follows that person. There is more but dont want to put in spoilers.

Both are by the same director and are crime shows. Also, both the female leads have a supernatural ability while the male leads are cops. (Black - she can forsee death, Voice - her hearing is more improved)

Black is about a detective possessed by the Grim Reaper. Ha Ram can see shadows of death. These two struggle to save the lives of people, breaking the rules of heaven.

Both dramas are about people who are all connected in mysterious ways and can see the missing dead.
In both dramas, one of the characters is a detective.

Both have body swap and there is area between afterlife and earth
But one is about revenge and normal life whereas the other is supernatural and ghosts.

Both stories are about grim reapers and souls. Black is a drama about a grim reaper that goes to the human realm in search of a soul he lost in the process he meddles with human affairs and remembers his past as a human. In "Along With the Gods" we see more of the other part of the grim reapers' job, guiding the souls through their next journey and eventual reincarnation, the main grim reaper, Gang Rim also interferes with the human "realm" because he has memories of his past self... In both there is a "mystery" that gets uncovered, although in AWtG is not as complex as in Black.
The two stories are different but have the same gist and give similar feelings. They both have great CGI and awesome acting.

Although Black has a supernatural element. Both dramas present a an interesting question.....who is this mysterious handsome man?

Both are mystery/thriller/suspense shows with both female leads being able to see/sense spirits who is accompanied with a supernatural detective whether he is death himself, the grim reaper (black) or a simple detective who died and came back as a spirit (the ghost detective) if you like mystery/supernatural then these are the shows for you.

They both have ghost seeing female leads, there is also a slight romance in both of them, they both also have similar/ the same genres

This drama is a love story between Kataoka Sakuya, a grim reaper who comes to the human world for the first time, and Mochizuki Nayuki, a woman who lost her father at a young age and has devoted her life to raising her only remaining family—her younger brother. As they meet, they gradually come to understand each other, and slowly, they begin to fall in love. However, a fate that will dramatically change their lives awaits them both…

In both shows, the Male Lead is a Grim Reaper tasked with fetching souls. One of these souls they are supposed to fetch is the Female Leads'. But, in trying to accomplish their goal, they end up falling in love with her instead.

DAYS feels way more lighthearted than Black, though. While the former starts with some hilarious comedy at first, halfway through the series the crime element of the show turns the series dark (pun intended).