There is same writer in both dramas. WCh is inspirated by north european thriller, WR is crazy korean romance, but in criminal line, you can see similarities.
A group of students are stuck in a situation & they all get to know everyone's true selves. In LB, the main leads are stuck in one of the friend's resort home. While WC the main characters are stuck in their school.
Both take place in a school setting. They've also got a mystery that the students are trying to solve on their own but as they dig deeper the mystery is stranger than anyone thought.
Both dramas are about a group of people getting a letter accusing them of having been a part of a murder/suicide which causes them to try and find out who truly killed the person/why the person committed suicide.
They both have a cast of unique characters solving a mystery in a location they can’t escape from. They also both start out somewhat slowly before delving into a story with plot twists and intrigue
It may not be similar plot line, but both dramas were made by director Kim Yong Soo, which means beautiful, artistic scenes and incredible soundtrack. Both really worth watching. :)