  We present comprehensive spectroscopic and photometric analysis of the
detached eclipsing binary KIC 12418816, which is composed of two very similar
and young main sequence stars of spectral type K0 on a circular orbit.
Combining spectroscopic and photometric modelling, we find masses and radii of
the components as 0.88+-0.06 Msun and 0.84+-0.05 Msun, and 0.85+-0.02 Rsun, and
0.84+-0.02 Rsun for the primary and the secondary, respectively. Both
components exhibit narrow emission features superposed on the cores of the Ca
II H&K lines, while H alpha and H beta photospheric absoprtion is more
completely infilled by broader emission. Very high precision Kepler photometry
reveals remarkable sinusoidal light variation at out-of-eclipse phases,
indicating strong spot activity, presumably on the surface of the secondary
component. Spots on the secondary component appear to migrate towards
decreasing orbital phases with a migration period of 0.72+-0.05 year. Besides
the sinusoidal variation, we detect 81 flares, and find that both components
possess flare activity. Our analysis shows that 25 flares among 81 come exhibit
very high energies with lower frequency, while the rest of them are very
frequent with lower energies.
