a) hiragana/ひらがな: phonetic alphabet. Most all hiragana characters are made up of one consonant and one vowel.
b) katakana/カタカナ: phonetic alphabet used for loan words
c) kanji/漢字: characters that come from China
d) romaji : Japanese also mix a bit of the roman alphabet
a) Japanese Hiragana (ひらがな) :
syllables developed from Chinese characters, as shown below. Hiragana were originally called onnade or 'women's hand' as were used mainly by women - men wrote in kanji and katakana. By the 10th century, hiragana were used by everybody. The word hiragana means "oridinary syllabic script".
b) Japanese Katakana (カタカナ):
The katakana syllabary was derived from abbreviated Chinese characters used by Buddhist monks to indicate the correct pronunciations of Chinese texts in the 9th century. At first there were many different symbols to represent one syllable of spoken Japanese, but over the years the system was streamlined. By the 14th century, there was a more or less one-to-one correspondence between spoken and written syllables.
The word katakana "part (of kanji) syllabic script". The "part" refers to the fact that katakana characters represent parts of kanji.
c) Kanji (漢字) :
The Chinese characters that are used in the modern Japanese logo-graphic writing system along with hiragana (ひらがな), katakana (カタカナ), Indo Arabic numerals, and the occasional use of the Latin alphabet (known as the Romanization of Japanese, or "Rōmaji"). The Japanese term kanji (漢字) literally means "Han characters".
c) Rōmaji (ローマ字) :
The romanization of Japanese is the use of the Latin alphabet ,Japanese is normally written in logographic characters borrowed from Chinese (kanji) and syllabic scripts (kana). The romanization of Japanese is done in any context where Japanese text is targeted at those who do not know the language, such as for names on street signs and passports, and in dictionaries and textbooks for foreign learners of the language.