  The T2K experiment has provided the first hint for the best-fit value for the
leptonic CP phase $\delta_{CP} \sim -90^\circ$ from neutrino data. This is now
corroborated by the NO$\nu$A neutrino runs. We study the implications for
neutrino mass hierarchy and octant of $\theta_{23}$ in the context of this data
assuming that the true value of $\delta_{CP}$ in nature is $-90^\circ$. Based
on simple arguments on degeneracies in the probabilities we show that a clear
signal of $\delta_{CP}=-90^\circ$ coming from T2K neutrino (antineutrino) data
is only possible if the true hierarchy is normal and the true octant is higher
(lower). Thus if the T2K neutrino and antineutrino data are fitted separately
and both give the true value of $\delta_{CP}=-90^\circ$, this will imply that
nature has chosen the true hierarchy to be normal and $\theta_{23} \approx
45^\circ$. However we find that the combined fit of neutrino and antineutrino
data will still point to true hierarchy as normal but the octant of
$\theta_{23}$ will remain undetermined. We do our analysis for both, the
current projected exposure ($7.8 \times 10^{21}$ pot) and planned extended
exposure ($20 \times 10^{21}$ pot). We also present the CP discovery potential
of T2K emphasizing on the role of antineutrinos. We find that one of the main
contribution of the antineutrino data is to remove the degenerate solutions
with the wrong octant. Thus the antineutrino run plays a more significant role
for those hierarchy-octant combinations for which this degeneracy is present.
If this degeneracy is absent, then only neutrino run gives a better result for
fixed $\theta_{13}$. However if we marginalize over $\theta_{13}$ then,
sensitivity corresponding to mixed run can be better than pure neutrino run.
