Both dramas feature a psychopath who tried to pursue a life that others may deem to not suit them due to the fact that they had an inability to feel any emotions or emphatize with other people. Both dramas had the main character ending up misdiagnosed while still young and growing up having traits of psychopathy inside them. Both dramas had the presumed psychopath character trying their best to break away from the stigma people had of psychopaths in general as they try to lead a normal life.
Both feature male nine-tailed foxes who ended up falling in love with humans and wanting to become humans. Both also featured nine-tailed foxes that became evil spirits due to an unfortunate circumstances in the past.
While the two shows dealt with different kinds of supernatural creatures aka gumiho and grim reapers, there's still a point of similarity between the two which was the Korean mythology involving the afterlife/underworld.
The two drama had an almost similar plot that is a doctor time-slipping between two different time periods. But in JIN's case, it was a modern doctor who ended up time-slipping towards the past. To be fair, I would've recc Dr. Jin that was a Korean adaptation of JIN for the sake of sticking to the same Korean setting but I might as well recc the original instead.
Both had a certain focus on dreams; on the main hero's conflicts about having given up on their dreams and later strive on to reclaim the dreams they used to have. Both movies also had another Ultraman being brought onto their worlds by a different party.
As I mentioned in my Tiga recommendation, it was also the same as for Ultraman Dyna. Since as with Katsumi, R/B's Minato Isami/Blu also had a lot of similarities shared with Dyna aka Asuka Shin. And alongside reference to plots from Ultraman Tiga, R/B also contained a lot of parallels from Ultraman Dyna as well. So I'm definitely recommending both series because of the huge homage R/B had in connection to the series.
The older brother of the Minato brothers, Minato Katsumi was quite similar to Madoka Daigo who is the protagonist in Ultraman Tiga. And if you love R/B's plot and characters, you'll definitely love Tiga as R/B did draw a lot of reference to the series. You might as well call R/B as a series homage to Ultraman Tiga.
While at first glance the two series may appear to not have a common trait, both series have a sole company that was responsible for the existences of Kamen Riders in their own universes. And while the Orphenochs and Humagears/Magears were exact opposites of each other (humans that were once dead and gained monster abilities versus human-like machines with an ability to turn into monsters once corrupted) their dilemmas and reasoning to revolt against Kamen Riders and humans, in general, were quite similar.
Both protagonist has supernatural abilities which later on ended up being used to help the police solve crimes. Both also deal with a complicated relationship with the main criminal whom the protag met during their childhood.
Both are mystery crime dramas where the lines and the roles between victims, investigators and assaillant/criminals are quite interchangeable and were quite blurred. Both dramas are very intriguing due to the fact you can never quite pinpoint who was it acting as an investigator, who were the victims and who were the true criminals as the truth ended up not being as straightforward as one had initially assumed. Also both dramas had Hirosue Ryoko playing as a victim character who ended up entangled in the many conspiracies in the dramas.
Both are adaptations from a manga that contained elements of time-travel. And amazingly enough, both also involved an incident set in Hokkaido while the protagonist was currently based in Tokyo. Also, both involved the protagonist being from a future with bad outcome ending up returning to the past to try to prevent incidents happening in order to change the past and future.
While one is a family of ninjas and the other is a family of magicians, the two series did still share a common trait which is a team of superheroes that shared familial bonds with each other who fights enemies who were born from the darkness as they try to cope with their every day lives. Not to mention there's a Magiyellow cameo as well as a sort of Magiranger parody in this. So if you like Ninninger or Magiranger when you watched it, you should be able to enjoy the other series as well.
