  Regardless of their different types of progenitors and central engines,
gamma-ray bursts (GRBs) were always assumed to be standalone systems after they
formed. Little attention has been paid to the possibility that a stellar
companion can still accompany a GRB itself. This paper investigates such a
GRB-involved binary system and studies the effects of the stellar companion on
the observed GRB emission when it is located inside the jet opening angle.
Assuming a typical emission radius of $\sim10^{15}\,$cm, we show that the
blockage by a companion star with a radius of
$R_\mathrm{c}\sim67\,\mathrm{R_\odot}$ becomes non-negligible when it is
located within a typical GRB jet opening angle (e.g., $\sim10$ degrees) and
beyond the GRB emission site. In such a case, an on-axis observer will see a
GRB with a similar temporal behavior but 25% dimmer. On the other hand, an
off-axis observer outside the jet opening angle (hence missed the original GRB)
can see a delayed "reflected" GRB, which is much fainter in brightness, much
wider in the temporal profile and slightly softer in energy. Our study can
naturally explain the origin of some low-luminosity GRBs. Moreover, we also
point out that the companion star may be shocked if it is located inside the
GRB emission site, which can give rise to an X-ray transient or a GRB followed
by a delayed X-ray bump on top of X-ray afterglows.
