is used before words that begin with a vowel sound. Since "Asian" starts with a long "A" sound ($/ˈeɪ.ʒən/), it requires "an." A is used before words that begin with a consonant sound. Example:

The choice between "a" and "an" depends on the sound of the following word:

Note: If the phrase is being used as a specific title or descriptor, the choice of article follows the same phonetic rule.

If you are asking about the grammatically correct article to use before the phrase "Asian shemale erect," the proper article is .

"I saw Asian shemale erect a new billboard." (Using 'erect' as a verb).