Honestly, the fact that Japanese has three systems of writinnever ceases to both amaze me and confuse me as to who thought of using three forms of writing and why they thought it was the best idea.... It was probably that people in Japan started using all three so they just all became standard Japanese.
I believe it's used in Katakana. There's 4 different sets of Japanese writing, so therefore... There's 4 different alphabets, Katakana, Hiragana, Kanji, and Romanji. Romanji is the easiest for foreigners to understand I guess, since it uses the English Alphabet.