  The origin of diverse nematicity and their order parameters in Fe-based
superconductors have been attracting increasing attention. Recently, a new type
of nematic order has been discovered in heavily hole-doped ($n_d=5.5$) compound
AFe$_2$As$_2$ (A=Cs, Rb). The discovered nematicity has $B_{2g}$ (=$d_{xy}$)
symmetry, rotated by $45^\circ$ from the $B_{1g}$ (=$d_{x^2-y^2}$) nematicity
in usual compounds with $n_d\approx6$. We predict that the "nematic bond
order", which is the symmetry-breaking of the correlated hopping, is
responsible for the $B_{2g}$ nematic order in AFe$_2$As$_2$. The Dirac pockets
in AFe$_2$As$_2$ is essential to stabilize the $B_{2g}$ bond order. Both
$B_{1g}$ and $B_{2g}$ nematicity in A$_{1-x}$Ba$_x$Fe$_2$As$_2$ are naturally
induced by the Aslamazov-Larkin many-body process, which describes the
spin-fluctuation-driven charge instability. The present study gives a great
hint to control the nature of charge nematicity by modifying the orbital
character and the topology of the Fermi surface.
