A variety of digital pets can be found in Japan, from virtual pets on palm-top game screens to physical entertainment robots. They are successful because they succeed in promoting a sense of reality in users' minds. While visual reality is a familiar element of realism, a subjective sense of reality can also prove effective. By designing interaction in a mode that takes users' psychology into account, such a sense of reality can be enhanced, especially when a user perceives an independent personality in his/her digital pet. Japanese traditional culture, which allows treating animals on an equal basis with human beings, is behind this psychology.