seems like WEP is about dealing with survivors guilt. All of them have in common a friend, family member that commited suicide. They blame themselves for it. They fight to save other suicidal people from their (literal) demons to cope, in the process learning why people are driven to the point of no return and learning more about themselves. Have a hunch that this constant fighting is gonna drive one of them to suicide, and the other three will have to fight their demons in a final boss kind of deal.
-Rika has a self harm scar already, cut marks on her wrist
-Neiru has a giant gash on her back
-Ai is wearing a sweater at almost all times. She is probably hiding something.
and Momoe is struggling with her gender and sexual identity. Her scars are more internalized, could lead to self harm as was the case one of the creators manga
this is a heavy theme to tackle. don't see a whole lot about self harm in anime. hope it sticks the landing, is able to deliver by the end in a way that makes sense.