  We use a recently proposed holographic Kondo model as a well-understood
example of AdS/boundary CFT (BCFT) duality, and show explicitly that in this
model the bulk volume decreases along the RG flow. We then obtain a proof that
this volume loss is indeed a generic feature of AdS/BCFT models of the type
proposed by Takayanagi in 2011. According to recent proposals holographically
relating bulk volume to such quantities as complexity or fidelity
susceptibility in the dual field theory, this suggests the existence of a
complexity or fidelity susceptibility analogue of the Affleck-Ludwig g-theorem,
which famously states the decrease of boundary entropy along the RG flow of a
BCFT. We comment on this possibility.
