U is a Japanese Kana pronounced 'ooh'. It can be represented by either katakana or hiragana.
Hiragana - う- This is my favorite hiragana to memorize. The long line is an old woman hunching her way down the street. Suddenly a brick falls on her back. she says, "Ooh!"
Katakana - ウ- I think of this as Ooh, look down there! (Looks like an arrow pointing down).
A relatively recent practice in Japanese is to add tentens (" Dots) to the katakana character and use it to express the V sound. It looks like this -ヴ- and is usually only used in Manga.