  We present the discovery of d1005+68, a new faint dwarf galaxy in the M81
Group, using observations taken with the Subaru Hyper Suprime-Cam. d1005+68's
color-magnitude diagram is consistent with a distance of $3.98_{-0.43}^{+0.39}$
Mpc, establishing group membership. We derive an absolute $V$-band magnitude,
from stellar isochrone fitting, of $M_{V} = -7.94_{-0.50}^{+0.38}$, with a
half-light radius of $r_{h} = 188_{-41}^{+39}$ pc. These place d1005+68 within
the radius-luminosity locus of Local Group and M81 satellites and among the
faintest confirmed satellites outside the Local Group. Assuming an age of 12
Gyr, d1005+68's red giant branch is best fit by an isochrone of [Fe/H] $= -1.90
\pm 0.24$. It has a projected separation from nearby M81 satellite BK5N of only
5 kpc. As this is well within BK5N's virial radius, we speculate that d1005+68
may be a satellite of BK5N. If confirmed, this would make d1005+68 one of the
first detected satellites-of-a-satellite.
