Recommendations

The leading men in both shows are so confident in their abilities and worth that doesn't realise their unfairness to others as it mostly doesn't came with a bad feeling, but is with a rather sharp tongue and judgement. Both consider themself elites. Both are somewhat abusive towards the female lead. Female lead in both is being considerate by them below their level and is a crybaby with a lot of troubles.

Both are recent office dramas which involve a somewhat unbelievable situations for examples of the struggles of the employers of the companies and have comedic aspects.

Both are office dramas, starring Ha Suk Jin in which he plays a somewhat despicable man (he is a better human in RO), while the female worker is honest and desperate by default (more desperate in DS)..

Both involve a female office worker who thinks she has a terminal illness and therefor start changing her attitude from a meek to a much more fighting one.. which starts changing her life.

The newer Let Ratree is a remake, the basic plotline is the same while some things were changed.

Both have male protagonists that are famous prosecutors who end up in prison. Both have top notch acting, intricate stories about crime, power, jealousy and revenge. The cast is amazing in both dramas.

Both revolve around cases of men framed and wrongfully sentenced to prison for having killed their family members. Both have prosecutors protagonists trying to uncover the truth, fighting the rich and powerful chaebols behind the case.

Both have male protagonists that were framed for their family murders and were unjustly imprisoned. They both struggle to bring the truth to light.

Both have a male protagonist that is a convicted swindler who gets out on parole with the excuse of taking care of a family member. Both undergo significant changes, as tragic challenges await for them outside of prison.
One is a drama, the other a movie.

Both about a weird teacher coming to a school to teach with a different style than all the other norm teachers. HAMMER SESSION is about getting the students to an elite school while Taiyo to Umi no Kyoshitsu is about keeping your good mark to get to your 1st choice school. In both dramas, the students learn to trust the teachers and learn a lot of moral lessons along the way.

Both dramas include lawyers who solve a crime that is close to home. In Defendant the victims were his wife and daughter whilst in Whisper the assailant is his new bride and her lover (so he his less inclined at the beginning to solve it). In both dramas they have a female helping them solve the crime. Both have similar feeling to them as well.

Both couples go through a lot to be together and face an illness.
(BOTH ARE REALLY SAD).
Have a box of tissues ready

Both follow the lonely lives of two social outcasts of different genders who end up finding and starting to love each other.

Even if Reply 1988 is korean and In Time With You is taiwanese, both of them are about family and relationships. There is the topic friendship turns into romance and also younger memories. Both of them are very enjoyable.

Both are about the main male lead time travelling. In Tunnel he goes to the future via a tunnel whilst in NNTTT he goes to the past via incense sticks. They both have to solve murder(s) whilst time travelling. A difference is that in NNTTT, the male lead can travel back and forth but only for a maximum of 30mins whilst in Tunnel he is stuck in the future and has to find a way back.