VI, 10, V, 11, __, 12, III. What number should fill the blank?

II
IV
IX
14

The answer is $\boxed{\text{IV}}$.

The sequence is a list of Roman numerals, each followed by a number one greater than the previous number. The Roman numerals are in reverse order, starting with $\text{VI}$ and ending with $\text{III}$. The numbers are in increasing order, starting with $10$ and ending with $12$.

Option $\text{A}$, $\text{II}$, is incorrect because it is not a Roman numeral.

Option $\text{B}$, $\text{IV}$, is correct because it is a Roman numeral that comes after $\text{III}$ and before $\text{V}$.

Option $\text{C}$, $\text{IX}$, is incorrect because it is not a number that comes after $10$ and before $12$.

Option $\text{D}$, $14$, is incorrect because it is not a Roman numeral.