Argthtjtr

I'm watching the anime ひぐらしのなく頃に. There's a character in it who greets people with おはようです. At first I thought it was just a cute affectation, but then I wondered, if おはようございます is okay then why not おはようです?

There seem to be quite a few hits on Google for this phrase. Is it a different level of politeness? Is it a regional thing or is it just weird?

I wondered, if おはようございます is okay then why not おはようです?

Grammatically, おはよう is a contraction of おはようございます, which is a Western dialect form otherwise should be おはやくございます in Standard Japanese. Since おはよう as such is not a valid word except for this fixed idiom, you can attach nothing to おはよう grammatically.

• ～うございます - keigo い-adjectives


• 
  Historical prospective of ウ音便 transformation (e.g. 有難く => 有難う))

Is it a different level of politeness? Is it a regional thing or is it just weird?

Contrary to what was said in the previous paragraph, strictly speaking, です is not prohibited to be attached to any phrases to make polite direct quotation out of them, and you can certainly treat it as a simplified polite ending by taking over this grammar. This usage is neither conventional nor standard in Standard Japanese, so you can think it of a mildly broken grammar. A girl speaks in off-point grammar is, some kind of, sign of cuteness.

• 
  ですの（ニコニコ大百科）

Additionally, some dialects indeed use this versatile です as their normal way of speaking. See:

• アニメキャラの「やってやるです」みたいな言い回しの文法性について（仮）


• ～するです。って方言ですか？

I think おはようです is a casual way of saying おはようございます and sensible adults don't use it , so you had better not use it to unfamiliar or elderly people. However you can use it to elderly people, if you are familiar with them.