キレイ is the first word I want to look at more closely because it was one of the few words we found that used katakana for emphasis purposes. It was found on the bottle of a Japanese Pantene Pro-V product. Unlike most of the words written in katakana, this word is clearly Japanese and is probably written like this to emphasize the effects of this products's purpose. For a person familiar with Japanese, katakana is probably an easy way to catch the attention of the reader because they probably encounter hiragana and kanji more frequently.
ルルルルルル is the second word I want to discuss because of the place I found this, my Nausicaa manga. The use of katanana here is also visually/artistically important, because it is fully integrated in the art. Unlike the text found in the dialogue bubbles, this katakana is easy to notice, usually because of the magnitude at which it appears on the page. At the same time, the use of katakana gives the sound effect a more unique feel because of katakana's scarce use.