  The ground and low-lying states of neutron-rich exotic Te and Sn isotopes are
studied in terms of the nuclear shell model by the same Hamiltonian used for
the spherical-deformed shape phase transition of Ba isotopes, without any
adjustment. An anomalously small value is obtained for $B(E2;0^+_1\to 2^+_1)$
in $^{136}$Te, consistently with a recent experiment. The levels of $^{136}$Te
up to yrast $12^+$ are shown to be in agreement with observed ones. It is
pointed out that $^{136}$Te can be an exceptionally suitable case for studying
mixed-symmetry 1$^+$, 2$^+$ and 3$^+$ states, and predictions are made for
energies, M1 and E2 properties. Systematic trends of structure of heavier and
more exotic Sn and Te isotopes beyond $^{136}$Te are studied by Monte Carlo
Shell Model, presenting an unusual and very slow evolution of
collectivity/deformation.
