Concept:
To solve definite integrals involving complex, symmetric fractional functions where standard algebraic integration looks impossible, we invoke King's Property of Definite Integrals:
\[
\int_{a}^{b} f(x) \, dx = \int_{a}^{b} f(a + b - x) \, dx
\]
Step 1: Applying King's Property to set up a twin integral equation.
Let our target definite integral equation be marked as \(I\):
\[
I = \int_{0}^{2026} \frac{x^5}{x^5 + (2026 - x)^5} \, dx \quad \cdots \text{(Equation 1)}
\]
Applying King's Property, we replace every instance of \(x\) across the function boundary with \((0 + 2026 - x) = (2026 - x)\):
\[
I = \int_{0}^{2026} \frac{(2026 - x)^5}{(2026 - x)^5 + (2026 - (2026 - x))^5} \, dx
\]
Simplifying the interior bracket terms yields:
\[
I = \int_{0}^{2026} \frac{(2026 - x)^5}{(2026 - x)^5 + x^5} \, dx \quad \cdots \text{(Equation 2)}
\]
Step 2: Adding both integral representations together.
Since Equation 1 and Equation 2 have identical upper and lower integration limits, we can sum their integrands directly:
\[
2I = \int_{0}^{2026} \left[ \frac{x^5}{x^5 + (2026 - x)^5} + \frac{(2026 - x)^5}{x^5 + (2026 - x)^5} \right] dx
\]
Notice that the numerators combine to perfectly match the common denominator:
\[
2I = \int_{0}^{2026} \frac{x^5 + (2026 - x)^5}{x^5 + (2026 - x)^5} \, dx
\]
\[
2I = \int_{0}^{2026} 1 \cdot dx
\]
Step 3: Integrating and isolating $I$.
Evaluating the simple integration constant across the limits:
\[
2I = \Big[ x \Big]_{0}^{2026} = 2026 - 0 = 2026
\]
\[
I = \frac{2026}{2} = 1013
\]