Both shows:
> Are set mostly in the hospital.
> Are melodramas.
> The leads are both doctors.
> The FLs are shown to struggle with a personal trauma that makes it hard for them to be a doctor.
> The MLs are smart, successful, and skillful.
> The FLs admire their superior and wish to learn from him. In DJ that superior is the ML, while in DR it's the 2ML.
> The Doctor in charge has been wrongfully accused at the start of the show. They are also both geniuses. They both have a "Dr. House" quality to them; with them being a bit impolite and eccentric in their actions.

Both shows:
>> Are heavy on the romance and are a light watch.
>> The MLs are wealthy and like taking care of the FLs.
>> Both leads meet briefly before ending up living in the same small town.
>> The FLs fall on hard times and try to find their purpose in a small town. In DDSSLLS the FL messes up during surgery and she ends up being sent away. In DDSSLLS the FL loses her dad and her dad's company and she ends up moving to a small town.
>> The MLs are lonely and they fall in love with the FLs first.
>> The MLs try to overcome a past trauma.
>> The FLs are warm and cheerful.

Both shows:
>> Are heavy on the romance.
>> Showcase a ML who falls in love with the FL quite quickly.
>> The Leads have a connection that's later found out.
>> The FLs used to be well-off but fall on hard times. In DJ the FL loses her fame due to a scandal. While in DDSSLLS the FL's father dies and she gets scammed out of her money.
>> The FL used to be renowned at the start of the drama. In DJ the FL was an actress, in DDSSLLS the FL was a pianist.
>> The ML comes from a wealthy family but he regards them almost as the enemy and keeps his distance.
>> The ML likes taking care of the FL. In DJ the ML sets an agency up for the FL; in DDSSLLS the ML sets the FL with her own piano academy.
>> There's a love triangle, but it gets dealt with quickly.
>> There's a secondary couple.

Both shows:
>> Shows an FL who relies on the ML at first.
>> The ML takes it upon himself to take care of the FL.
>> Both leads establish a strong friendship.
>> The ML falls in love with the FL first and pursues her.
>> The ML are loners before meeting the FLs. However, they both have an older man who they consider almost a fatherly/grandfatherly figure lend them a hand.
>> The ML ends up teaming up with a group of misfits.
>> BIOG has a darker plot than DDSSLLS.

Both shows:
>> Feature a kind of time travel. In Kairos, the ML is able to change his present by having the FL (who is one month in the past) change things. In 365, both the ML and FL travel back one year to change the outcome of their lives.
>> The ML is betrayed by someone close.
>> The ML and FL must work together to overcome a common thread.
>> The FL is actively engaged in the plot and knows how to overcome problems.
>> The leads establish a deep friendship.
>> The ML in 365 RTY has a group of friends he relies on; while the FL in Kairos has a similare net of support as well.

The thing that ties these two shows together is the love triangle aspect. In both shows, you have the ML and FL establish a deep bond when they were children, but they get separated.

Once they grow up, one of the leads (FL in SU and ML in SWP) tries to find their childhood love and reconnect. However, instead of meeting them honestly, the other main lead (ML in SU and FL in SWP) asks someone else (2ML in SU and 2FL in SWP) to "pretend to be them" and meet with the now successful lead (FL in SU and ML in SWP).

However, unintendedly, the second lead ends up developing feelings for the main lead, extending the lie while giving room for the main leads to fall in love with each other.

Both shows deal with characters in different time lines affecting a case. In Tunnel, the ML travels from the past into the future. In Kairos the ML is in the future but can communicate via a phone with the FL who is one month in the past.

Both shows feature a character who is a zombie. Not only do they need to learn to control their instinct to eat, but they do not remember why, how or who killed them.

In ZD the ML is the zombie, while in AKO the 2FL is the zombie. They each end up finding a close friend who helps them through their ordeal.

They also both:
> Use dark comedy and push the absurd flawlessly within the plot.
> They embrace k-drama tropes, make fun of them yet simultaneously using them to further the plot.
> Have eccentric and unique Male Leads and quirky Female Leads.
> The Female Leads are active in the plot and strive to uncover mysteries. They are both skillfull and stubborn.
> The Leads establish a deep sense of friendship with a subtle hint of romance between them.
> The main antagonist is a serial killer, though in PD he's more prominent than in ZD.
> These two shows make for a light and entertaining watch.

In both shows:
> The Female Lead has the ability to see ghosts. In Black she's born with the ability, whereas in TOTNT she developes/is given the ability.
> The Male Leads have few friends.
> The Male Leads are't human. In Black he's a grim reaper and in TOTNT he's a fox.
> The Male Leads are constantly protecting the Female Leads, more so when they develop feelings towards them.
> The Male Leads are strong, cocky but hilarious.

Having said that, Black is a lot darker than TOTNT.

The shows are similar in the following themes:
> The Female Lead must navigate a world that feels different from her own and, therefore, she ends up relying on the Male Lead's help and guidance.
> Both leads grow up in a rich family.
> The Male Lead isn't as honest with his feelings towards the Female Lead at first. Though in both cases, their actions are more honest than their words.
> The Male Lead chases the Female Lead first.
> One of the leads is a successful piano player. In CL, it's the ML while in DDSSLLS it's the Female Lead.
> The Female Lead is a bit spoiled but in a fun way.
> The Female Lead is betrayed by someone close to her.
> The Leads met each other prior to the start of the show, with the ML remembering that encounter before the FL does.
> The ML lost someone really important before the start of the drama, which still causes him pain.
> The FL lost her birthmother when they were young.

The shows are quite different, but they do touch upon various similar themes:
> The Female Leads are ambitious and persistent. They don't only dream big, but they show they have the skills to ground those dreams and make them a reality. They are also undervalued by others and judged harshly for their backgrounds, but they show they don't care what others think as they walk to the sound of their own drums.
> The Male Leads are shown to be good at what they do, but they lack the tooth to make it big on their own, which is where the FL comes in. They end up trusting and almost following the Female Lead as they go forward.
> They both culminate in becoming partners in their own company.
> The relationship between the leads also begins with a lie. In Hyena, the FL lies to the ML and pretends to be someone she's not. Whereas in Start Up, the ML lies to the FL and pretends to be someone he's not.
> There are more than two strong female leads within the show who are strong, independent and actively involved in the plot.