Role Reversal Letter-writing (RRLW) is a multidisciplinary technique that has the potential for use in conjunction with various theories of psychotherapy. However, its theoretical development has been slow, partly because it originated in a specific theoretical background in the field of justice and crime in Japan. Therefore, it is necessary to understand RRLW as a group of techniques with many variations beyond a certain theoretical background or field of study, and to construct a theory of these techniques. This study has divided the techniques into three functions of psychotherapy: 1) unfinished business, 2) self-care for hurt and confusion, and 3) self-organization of inner conflicts, and has discussed the characteristics of each function. The uniqueness of the letter use is that it creates a time and space shift, a perceptual shift, and a shift between ordinary and extraordinary, and guarantees the ritualistic, unusual, and confidential functions of the RRLW. Compared to the Empty Chair, the RRLW is particularly suited to unfinished business, staying in an experience and reflecting, organizing multiple aspects of the self, and acquiring self-care.