This paper describes the rapidly evolving and unusual supernova LSQ13ddu , discovered by the La Silla-QUEST survey .
LSQ13ddu displayed a rapid rise of just 4.8 \pm 0.9 d to reach a peak brightness of - 19.70 \pm 0.02 mag in the LSQgr band .
Early spectra of LSQ13ddu showed the presence of weak and narrow { \mathrm { He \mathsc { i } } } features arising from interaction with circumstellar material ( CSM ) .
These interaction signatures weakened quickly , with broad features consistent with those seen in stripped-envelope SNe becoming dominant around two weeks after maximum .
The narrow { \mathrm { He \mathsc { i } } } velocities are consistent with the wind velocities of luminous blue variables but its spectra lack the typically seen hydrogen features .
The fast and bright early light curve is inconsistent with radioactive ^ { 56 } Ni powering but can be explained through a combination of CSM interaction and an underlying ^ { 56 } Ni decay component that dominates the later time behaviour of LSQ13ddu .
Based on the strength of the underlying broad features , LSQ13ddu appears deficient in He compared to standard SNe Ib .