The greatest and most awful evil in the schoolboy code
in a classic school story. An informant
has sinned against the Nakama
and will forever receive a Mark of Shame
This can be handled in various ways. Sometimes the Aesop of the story is that there are times to inform as when the other student is cheating or "doing something harmful to himself".
In the Crime and Punishment
genre, this is the most important part of Honor Among Thieves