What's up with the name "Zerozaki Hitoshiki"?
As @ʞɹɐzǝɹ mentions, the kanji 零 can be read as ぜろ ("zero") and has the meaning "null" or "cipher", as well as "overflow" (as in the word こぼれる). 崎 can be read as さき ("saki") which can become "zaki" under rendaku. It's the same kanji we see in common spellings of the names "Yamazaki" and "Kanzaki" (山崎 and 神崎). I believe this might be to make the word sound more like a real name, like adding Mc- or -son to English words ("Grumpy McSnarlson"). 

人識 ("Hitoshiki"), the character's given name, is written with the kanji for "person" (hito) and "know" (識) (also seen in the word shiru). Again, I believe the 識 character is just to make the name sound more like a name. The fact that he kills people may lend some significance to the 人 kanji.