Complete the sequence: ZA8, Y7B, XC6, W5D, _?_

Let's split the alphanumeric sequence into three separate series component-wise:
1. First Letter Series (Z, Y, X, W, ...):
Decreasing backward alphabet sequence: Z $\to$ Y $\to$ X $\to$ W $\to$ V
2. Middle Number/Letter Element:
Notice the middle element alternates positions and values:
* Term 1: Letter 'A' is at position 2 ($2\text{nd}$ spot).
* Term 2: Number '7' is at position 2 ($2\text{nd}$ spot).
* Term 3: Letter 'C' is at position 2 ($2\text{nd}$ spot).
* Term 4: Number '5' is at position 2 ($2\text{nd}$ spot).
* Following this alternation, Term 5 must have a Letter at position 2. The letters sequence is A $\to$ B (at end) $\to$ C $\to$ D (at end) $\to$ E (should be at position 2).

3. Third Element Series:
* Term 1: Number 8 (at end)
* Term 2: Letter B (at end)
* Term 3: Number 6 (at end)
* Term 4: Letter D (at end)
* Term 5 must have a Number at the end. The numbers sequence is $8\to 7\to 6\to 5\to 4$.

Combining the elements for Term 5: First letter is V, middle element is letter E, and final element is number 4. Thus, the next term is VE4.