Katakana
The system of Katakana is similar to Hiragana. Together they're known as Kana and were originally based on the Kanji symbols which existed more than one thousand years ago. Since than they've developed into their present form and both Hiragana and Katakana each have their own set of 46 symbols with which to form their words.
The system of Katakana symbols is used almost exclusively to represent words that are non Japanese in origin. These symbols are similar to the system of hiragana with the main difference being that words in Katakana have sharper edges and are much more angular in appearance.
And that concludes the three types of Japanese tattoo symbols that are available. However, there's no rule that says you have to choose one style and stick to it. You could have your tattoo designed so that it includes more than one of these styles. For example, you could have a sentence written using Hiragana that includes various Kanji symbols to enrich it with greater meaning.
But whatever option you select, it's important to take one additional safety precaution before you go anywhere near a tattoo studio with your design. As you can see from this brief explanation of different character types, the system of Japanese writing is extremely complicated and subtle.