They are both similar to eachother with the storyline and they are both kdramas that have the same stories which are similar.

these 2 kdramas have almost the exact storylines because they are both about a person who got bullied and wants to take revenge on them .

now 20th century girl kind of similar to this kdrama because it shows that the main female lead missed their partner because of the same reason which is death and the side couple of this kdrama (seaons of blossoms )which was bomi and jinyong has also the same storyline of 20th century girl beacause in 20th century girl the main female lead liked this boy but her bestfriend also liked him.

it is similar to extraordinary you because they are both in comic book and the storyline is almost the same.

it is kinda similar in plot but to be honest I don't know why, I just kind of got that kdrama 'Splash Splash Love' vibes from watching it.