(When romanizing words in Japanese, I used contemporary Japanese spelling wherever possible and avoided more correct spelling according to historical linguistics, in order to avoid some complexity not relevant to the main line of exposition.)
Early Development, Kanji, Man'yōgana, Katakana, and Hiragana
The decision to write Japanese using Chinese characters--or kanji--was not made with the conscious knowledge of the repercussions that the decision would later entail. If the question of adopting a foreign script like Chinese (which is linguistically not similar to Japanese at all) were under consideration today, the Japanese would certainly not consent to such an adventure. Anyone studying Japanese now can attest to the awkwardness and the challenge the Japanese writing system poses. This is true not only for learners of Japanese as a foreign language but for Japanese themselves. It might be of interest to trace the history of the writing system and find out how, like anything else adopted from a foreign land, the Chinese writing system was modified to fit the Japanese language.
A Chinese book entitled Gokansyo waden 後漢書倭伝, dated A.D. 57, tells of a country to the east of China. This description presumably refers to a part of present-day Japan, probably in the island of Kyūshū. This area was apparently ruled by a king and therefore, we may assume, this country had a structured socio-political life. This very early description of Japan received more credence when a Chinese gold seal was unearthed in 1784 in Fukuoka, a city in northern Kyūshū. Measuring 2.3 cm x 2.3 cm x 0.8 cm and weighing 109 g, it bore the inscription kan no wa no na no kokuō 漢委奴国王 "King of the country of Wa, tribe Na, under the Han rule." This seal is thought to be one that the Tang Emperor Kōbu 光武帝¸ (the first emperor of the Late Han Dynasty, 6 B.C.- A.D. 57) presented to the Japanese emissary. It is therefore plausible that contact between China and Japan existed around the beginning of the Christian era. And by implication, it is possible that the practice of adopting Chinese to write Japanese began around this time.
On the other side of the Japan Sea, other records are useful in learning more about how kanji was adopted. According to the description in the Kojiki and Nihonshoki, kanji were brought from China during the reign of Emperor Ōjin ((王神天皇, fifth century A.D.) by a man named Wani (王仁) from the Korean kingdom of Paekche (Ch. 百済, Jp. Kudara), one of the three major political states then occupying the Korean Peninsula. Wani is said to have brought the ten-volume Analects of Confucius 論語 and Senjimon 千字文, a textbook for learning and teaching kanji. Wani is credited with teaching kanji to the imperial prince Uji no Wakiiratsuko 菟道稚郎子.
It was not until the fledgling country of Japan sent scholars to China for study beginning around A.D. 600 that the effort to write Japanese in Chinese began in earnest. These scholars were called kenzuishi or kentōshi. Kenzuishi means "emissaries to the Dynasty of Sui (589-619)" and kentōshi means "emissaries to the Dynasty of Tang (618-907)." Until the program was abolished in A.D. 894 because of political instability in the Tang dynasty, the Japanese government sponsored more than ten trips, each trip numbering between 500 to 600 bureaucrats and scholars who would stay in China for two to three years to learn and observe all they could in one of the most civilized cultures in the world. At the conclusion of their studies, the students returned to Japan with documents of all sorts, including Buddhist scriptures written in Chinese. It is these Buddhist scriptures that served as the major seed for the development of the Japanese writing system.