  We clarify the origin of the anomalously hindered $E2$ decay from the $4^+_1$
level in $^{44}$S by performing a novel many-body analysis in the shell model.
Within a unified picture about the occurrence of isomerism in neutron-rich
sulfur isotopes, the $4^+_1$ state is demonstrated to be a $K=4$ isomer
dominated by the two-quasiparticle configuration
$\nu\Omega^{\pi}=1/2^-\otimes\nu\Omega^{\pi}=7/2^-$. The $4^+_1$ state in
$^{44}$S is a new type of high-$K$ isomer which has significant triaxiality.
