Japanese given names are composed of one or more kanji (though a few are written in hiragana), meaning there are thousands of possible names. Many kanji are pronounced the same way, with the result that a single name might be spelled differently by different people. Further complicating the situation is the fact that an individual kanji can have several different readings (pronunciations). For example, 海 meaning "ocean" can be read umi or kai depending on context and other factors. Some kanji have nanori, which are readings which occur only in names. See kanji readings for more information.
What this means is that in practice it is not possible to determine how a person's name is pronounced based on the spelling, nor is it possible to determine the spelling based on the pronunciation. Sometimes written names include furigana, which are small hiragana characters above the name indicating the pronunciation.
In the past, boys were sometimes given names indicating the order in which they were born, for example Ichirou "first son" and Jirou "second son". In girls' names, a common final Kanji was 子 ko meaning "child" (for example Akiko and Yoshiko), though this trend has faded in the last few decades.