  From long-term photometry of a VY Scl-type star, V425 Cas, between 1998 and
2000, we discovered a short-term, large-amplitude (up to 1.5 mag) variations.
The variation was well represented by a single period of 2.65 d. The large
amplitude and the profile of the folded light curve suggest that the dwarf
nova-type disk instability is responsible for this variation. The shortness of
the period is unprecedented in hydrogen-rich cataclysmic variables. Given the
recent emerging evidence that the irradiation from white dwarfs in VY Scl-type
systems affect their light behavior, we propose a possibility that this unique
variation in V425 Cas can be explained by the combination of the dwarf
nova-type disk instability and irradiation. Similar short-period "outbursts"
have been known in X-ray transients (V518 Per), and helium cataclysmic
variables (CR Boo and V803 Cen). We discuss the possibility that these
phenomena have a common origin to the unique variation in V425 Cas.
