Solution to the iterative differential equation $-\gamma g' = g^{-1}$

Using a Picard-like operator $T$, we prove that the iterative differential equation $-\gamma g' = g^{-1}$ with parameter $\gamma>0$ has a solution $g=h\colon[0,1]\to[0,1]$ for only one value $\gamma=\kappa\approx0.278877$, and that this solution $h$ is unique. As an even stronger result, we exhibit $h$ as the global limit of the operator $T$.