  We investigate the nonlinear dynamics of D=2N+3 Myers-Perry black holes with
almost equal angular momenta, which have N equal spins out of possible N+1
spins. In particular, we study the ultraspinning instability and the fate of
its nonlinear evolution using the large D effective theory approach. We find
that every stationary phase can be mapped to the counterpart in the singly
rotating phase within the leading order effective theory. From the known
results of singly rotating solutions, we obtain the phase diagram of almost
equally rotating black holes. We also obtain a certain implication for the
possible topology changing transition.
