>>86739590>>86743999There is actually no rule on the use of hiragana vs katakana. It's common for native words to be written in hiragana, but the language allows writing them in katakana too. There are many reasons why someone would want to do that and all of them can be summarized as "I felt like it".
Some examples as to why one would want to use katakana instead of hiragana for native words: for emphasis on a flyer; it's faster to write by hand so waiters might use it to take orders; it's a speech bubble for a robot in a comic who doesn't have a "natural flow"; it's used as "uppercase" on the web.
As a side note, certain words despite being listed in online dictionaries as having kanji, are actually written only in kana. A famous example is こんにちは which doesn't have an associated kanji sequence; the one you see online, 今日は, means "today".
