What's the difference between きみ and 君?

Question:

They both mean "you" (kimi), right? What is the difference?

Answer:

きみ is in Hiragana.
君 is in Kanji.

You should use the Kanji character though.
They are the same word except people don't use "きみ" because the proper way is to use the Kanji.

It means "You".
Usually it is said by males speaking to a female or someone younger than themselves.