I've noticed sometimes, especially in video games, that some parts of sentences that would normally be written in hiragana is instead written in katakana. For example, I've seen "です" written as "デス" and even words being split into hiragana and katakana "pieces" such as "ください" written as ”くだサイ". So why would this be used? Could it be just random and discretionary, or could it convey something specific to the reader e.g. in/formality?