• 君きみ — you
• 君主くんしゅ — monarch
• 君達きみたち — you all
• 君子くんし — nobleman
• 君命くんめい — imperial order
• 暴君ぼうくん — tyrant; despot

君 combines 口 (mouth, command) with 尹 (to rule), giving it the sense of a person who rules by word or command — hence, a lord or ruler. Over time, it also came to be used affectionately to refer to someone personally (like “you” or “buddy”).