I've looked over using Katakana in modern Japanese. As a result, I can summarize the role and function of Katakana in inscription of Japanese as following.
1. By giving a point, the word has an effect that can emphasize meaning and image. Inscription of Katakana expresses not only emphasizing specific words but also pointing accurate areas by exposing visual image.
2. In contrast with an emphasizing effect, I identified Katakana as a role which alleviates minus image of meaning of meaning and its image in Slang.
3. If someone wish to express either positive emotion or negative one, and when someone uses means of evaluation.
4. Katakana which already offcialized is used to change difficult chinese characters by Japanese.