The Japanese astrophysical payload MAXI (Monitor of All-sky X-ray Image) has been monitor- ing the variable X-ray sky since August 15, 2009 from the International Space Station. With the 10 year’s unbiased survey, the nature of the largest stellar flares and the hosts have been gradually revealed. We recognized that the flares, which MAXI detected, are occurred from limited number of active stars repeatedly, and most, so called "active stars" are quiet in MAXI’s monitoring. It is notable that the most energetic flare source in the MAXI sample is the quadruple system GT Mus, which is located at 109.594 pc distance (Sasaki et al. 2020). We will review the MAXI monitoring of GT Mus. We also introduce the follow-up observation with NICER.