Japanese alphabet is called kana (it means letter). Because kana is not separate consonet and vowel, it needs little more characters. For example, a, i, u, e, o are placed left most column in the keyboard, ka, ki, ku, ke, ko were placed next column of a-i-u-e-o. the next next column is sa-shi-su-se-so, ans so forth. In the school of Japan, 50 sound table was taught. The very keyboard has the same arrangement of that table. I think it has no more meaning, in the sense of ergonomics.