  Pairs of misalignment-produced axions with nearby masses can experience a
nonlinear resonance that leads to enhanced direct and astrophysical signatures
of axion dark matter. In much of the relevant parameter space,
self-interactions cause axion fluctuations to become nonperturbative and to
collapse in the early Universe. We investigate the observational consequences
of such nonperturbative structure in this "friendly axion" scenario with $3+1$
dimensional simulations. Critically, in a substantial fraction of parameter
space we find that nonlinear dynamics work to equilibrate the abundance of the
two axions, making it easier than previously expected to experimentally confirm
the existence of a resonant pair. We also compute the gravitational wave
emission from friendly axion dark matter; while the resulting stochastic
background is likely undetectable for axion masses above $10^{-22} \,
\text{eV}$, the polarization of the cosmic microwave background does constrain
possible hyperlight, friendly subcomponents. Finally, we demonstrate that
dense, self-interaction--bound oscillons formed during the period of strong
nonlinearity are driven by the homogeneous axion background, enhancing their
lifetime beyond the in-vacuum expectation.
