  We first point out to all order $\alpha'$ corrections to lower order
fermionic couplings and their effective actions of type II super string theory.
In order to reveal all symmetries of the particular D-brane Anti-D-brane
system, and to construct not only all the singularity structures but also all
order $\alpha'$ corrections of fermionic couplings to tachyons, we employ all
the Conformal Field Theory (CFT) methods to a six point function. Basically, we
construct all the correlation functions of four spin operators and two world
sheet fermion fields. The S-matrix of two fermion fields, two real tachyons in
the presence of a closed string Ramond-Ramond (RR) field in type II will be
explored. Applying all the symmetries of the amplitude, a proper expansion for
D-brane Anti D-brane is also found out. Having carried out all the Effective
Field Theory (EFT) techniques, one would discover all order singularity
structures of string theory. The entire algebraic computations of the amplitude
of $<V_{C^{-1}(z,\bar z)} V_{\bar\psi^{-1/2}(x_1)} V_{\psi^{-1/2}(x_2)}
V_{T^{0}(x_3)} V_{T^{0}(x_4)}>$ have also been derived. Various new string
couplings are revealed as well. Eventually, making comparison the S-matrix with
all EFT parts, all order $\alpha'$ higher derivative corrections to two
fermions -- two tachyons in the world volume of D-brane Anti D-brane of type II
are discovered accordingly.
