As there are thousands of characters including Chinese characters in Japanese writings, it is necessary for typing Japanese at a keyboard to convert to specific words from kana inputted firstly. To do so, kana-kanji conversion system is the common method, and roman character input and kana input are conducted before this conversion system.
Roman character input is the most popular at typing Japanese at a keyboard. In this input, firstly roman characters are inputted and then converted to kana characters. It is easy to master this method if learners know typing of QWERTY keyboard and roman characters. Only 26 alphabets are used in this input. Thus, the majority uses this roman character input. International students in Japan also might as well master this method at first.
Although kana input requires keyboards which have kana keys, it is possible to type faster because it requires fewer key entries. As a result, the users are less likely to get tired. Thus, it is said that kana input is used by some professionals such as journalists who need to type fast and a lot.