The highly modulated optical light curve of HD 79826 (spectral types G5+M5) was discovered in the \chan guide-star light curves, indicating a period of about 0.5 days, a strong and migrating distortion wave, and a shallow eclipse. We subsequently obtained simultaneous \chan high resolution X-ray spectra and optical photometry, along with contemporaneous ground-based photometry and spectra. X-ray rotational or eclipse modulation was totally obscured by X-ray variability and flares. X-ray spectra are characterized by coronal emission near the saturation limit of L_{x}/L_{bol} = 10^{mthree}. Optical spectra show extremely rotationally broadened features, variable with orbital phase. Optical light curves show the modulation to be not only rapidly migrating in phase, but also of variable amplitude. We characterize the X-ray emission through measurements of line widths, velocities, and fluxes, and provide coronal plasma models. This star is near or at the limits of dynamo saturation, and since it is partially eclipsing, has potential to be well characterized in terms of fundamental stellar parameters.