  We consider string theory in maximally supersymmetric type IIB plane wave
background with constant five form Ramond-Ramond flux (RR plane wave). It is
argued that there exists a universal sector of string configurations
independent of the null coordinate $x^-$ such that the space-time action
evaluated at such a configuration is same in the RR plane wave and flat
background. By naturally assuming its validity for the open strings we further
argue that the D-branes extending along $x^{\pm}$ are universal in these two
backgrounds. Moreover, a universal D-brane which is BPS in flat space must be
tachyon-free in RR plane wave and a non-BPS D-brane should have a real tachyon
whose potential is universal. Given the above observation we then proceed to
describe open string theories for the non-BPS D-branes in RR plane wave. It is
suggested that the light-cone Green-Schwarz fermions on the world-sheet satisfy
certain bi-local boundary condition similar to that corresponding to flat
space. We attempt a canonical quantisation with this boundary condition which
gives rise to an open string spectrum similar to that in flat space -
containing an R and NS sectors of states. In this process we encounter certain
subtleties involving the R sector zero modes. Although the derivation of the R
sector zero mode spectrum using the open string theory has not been completely
settled, we suggest definite answer by requiring consistency with the relevant
space-time interpretation. We finally generalise the above basic features of
universality to all the exact pp-wave backgrounds with the same dilaton profile
in a given string theory.
