Find the missing character?

The missing character is $\boxed{\text{W}}$.

The other three characters, $A$, $C$, and $I$, are all vowels. Vowels are letters that make a sound when you say them, and they are used to make words. The letter $W$ is not a vowel. It is a consonant. Consonants are letters that make a sound when you say them, but they are not used to make words by themselves. They need to be combined with vowels to make words.

Here are some examples of words that start with the letter $W$:

• Water
• Walk
• Window
• Watch
• World

Here are some examples of words that end with the letter $W$:

• Saw
• New
• Dew
• Few
• Sew

Here are some examples of words that have the letter $W$ in the middle:

• About
• Cow
• How
• Now
• Town