Recommendations

Both depict a mother and son with a strained relationship that turns incestuous.

Both depict extreme cases of a teenage boy being bullied by his classmates. No one helps or believes them, and even their own mothers abuse them from time to time.

Both depict quiet teenage boys who struggle with loneliness and survival.

The tone of the drama is similar. Few words are repeatedly used by the main leads in all the episodes. Both dramas doesn't proceed in the way you expect it to be.

As "That's Cunning! Shijo Saidai no Sakusen", "Bad Genius" is a film about cheating in exams to achieve a goal.
In the first one, the goal is to protect their dorm. In "Bad Genius" the goal is to complete the task in order to receive money.

Both of them are about people cheating in exams, Although they don't have the same motivation or objective to cheat.

Both feature a main character that faces (potential) discrimination because of their social background--burakumin in Japan and baekjong in Korea.

Both dramas are heartwarming and heartbreaking as the main character overcomes adversities with the help of cell mates while in prison

both are focused on the draft day where 21 year old males participate in a lottery that determines wether they have to join the military or not. Theyre also both lgbt themed and directed by Josh Kim

Both stories are about three working women in Shanghai turning thirty and having problems in both their love lives and careers.

Both are about a young boy struggling to survive without parents.

* female leads are divorced
* female leads wants the custody of their child so do a 24/7 job
* female leads are older than the male leads
* female leads are employees of males leads

if you liked Tell me what you saw i am sure you gonna like Class of lies too, that's my opinion.
Class of lies is about a highly successful lawyer who falls from grace because of one case. He becomes a fixed term teacher at a high school that is tied to that case in order to regain his honor. Though he goes into the classroom for selfish reasons, he begins to see the crimes that take place and he takes matters into his own hands to help protect victims from their peers. The drama will shine a spotlight on the reality of teenagers facing little to no repercussions after committing a crime because they are teenagers, providing no protection for those who become a victim to these crimes. (Source: Soompi)
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Tell me what you saw is about Oh Hyun Jae who used to be a top criminal profiler. He solved many cases with his skills, but one day an explosion, caused by a serial killer, ended the life of his fiancé. After the horrific incident, Oh Hyun Jae vanished and he now lives in seclusion. Meanwhile, Cha Soo Young is a police officer in the countryside. She has a special ability which allows her to remember exactly everything she sees. Due to her special ability, she is selected as a rookie detective who will partner with Oh Hyun Jae informally. Together they work to solve cases and uncover the truth behind the Peppermint Killer, the resurfaced serial killer who murdered Hyun-Jae's fiancé five years ago.
(Source: AsianWiki)

While in itself being quite different ( Mermaid mystery vs. BL drama) they both share a plot of reincarnation and rediscovering the past memories and the hidden conspiracies around their past selves. I really love both of them a lot and rewatched them several times. If you are looking for something fresh and fluffy, check them out!

The disguised superhero with a double life is probably my favorite trope ever, and it shows up in both of these.