Yuta Notsu is studying solar and stellar magnetic activities especially "superflares" on solar-type (G-type) stars and cooler K,M-type stars, using the various photometric and spectroscopic data from space and ground telescopes (e.g., Kepler, TESS, XMM-Newton, NICER, Swift, HST, APO3.5m, SMARTS1.5m, Seimei 3.8m). Through these observational studies, I investigate how multi-wavelength stellar flare emissions occur in the stellar atmosphere (photosphere - choromosphere - corona), how stellar CMEs occur, and how planets (e.g., Earth, Mars, exoplanets) are affected from these flares and CMEs.