  Magnetospheric accretion has been thoroughly studied in young stellar systems
with full non-evolved accretion disks, but it is poorly documented for
transition disk objects with large inner cavities. We aim at characterizing the
star-disk interaction and the accretion process onto the central star of LkCa
15, a transition disk system with an inner dust cavity. We obtained
quasi-simultaneous photometric and spectropolarimetric observations of the
system over several rotational periods. We analyzed the system light curve, as
well as changes in spectral continuum and line profile to derive the properties
of the accretion flow from the edge of the inner disk to the central star. We
also derived magnetic field measurements at the stellar surface. We find that
the system exhibits magnetic, photometric, and spectroscopic variability with a
period of about 5.70 days. The light curve reveals a periodic dip, which
suggests the presence of an inner disk warp that is located at the corotation
radius at about 0.06 au from the star. Line profile variations and veiling
variability are consistent with a magnetospheric accretion model where the
funnel flows reach the star at high latitudes. This leads to the development of
an accretion shock close to the magnetic poles. All diagnostics point to a
highly inclined inner disk that interacts with the stellar magnetosphere. The
spectroscopic and photometric variability of LkCa 15 is remarkably similar to
that of AA Tau, the prototype of periodic dippers. We therefore suggest that
the origin of the variability is a rotating disk warp that is located at the
inner edge of a highly inclined disk close to the star. This contrasts with the
moderate inclination of the outer transition disk seen on the large scale and
thus provides evidence for a significant misalignment between the inner and
outer disks of this planet-forming transition disk system.
