Authors: Yuta Notsu (CU Boulder/LASP/NSO), Adam F. Kowalski (CU Boulder/LASP/NSO), Hiroyuki Maehara (NAOJ), Kosuke Namekata (NAOJ), Kenji Hamaguchi (NASA/GSFC & UMBC), Teruaki Enoto (Kyoto University), Isaiah I. Tristan (CU Boulder/LASP/NSO), Suzanne L. Hawley (University of Washington), James R. A. Davenport (University of Washington), Satoshi Honda (University of Hyogo), Kai Ikuta (University of Tokyo), Shun Inoue (Kyoto University), Keiichi Namizaki (Kyoto University), Daisaku Nogami (Kyoto University), Kazunari Shibata (Kyoto University)

We conducted the time-resolved simultaneous optical spectroscopic and photometric observations of mid M dwarf flare stars YZ CMi, EV Lac, and AD Leo. Spectroscopic observations were obtained using Apache Point Observatory 3.5m and Small \& Moderate Aperture Research Telescope System 1.5m telescopes during 31 nights. Among the 42 detected flares, seven flares showed clear blue wing asymmetries in the H$\alpha$ line, with various correspondences in flare properties. The duration of the blue wing asymmetries range from 20 min to 2.5 hours, including a flare showing the shift from blue to red wing asymmetry. Blue wing asymmetries might be observed more frequently during non-white-light flares. All of the seven flares showed blue wing asymmetries also in the H$\beta$ line,  but there are large varieties on which other chromospheric lines showed blue wing asymmetries. One among the 7 flares was also observed with soft X-ray spectroscopy, which enabled us to estimate the flare magnetic field and length of the flare loop.  The line-of-sight velocities of the blue-shifted components range from -73 to -122 km s$^{-1}$. Assuming that the blue-shifts were caused by prominence eruptions,the mass of upward moving plasma was estimated to be 10$^{15}$ — 10$^{18}$ g, which are roughly on the relation between flare energy and erupting mass expected from solar coronal mass ejections (CMEs). Although further investigations are necessary for understanding the observed various properties, these possible prominence eruptions on M-dwarfs could evolve into erupting CMEs, and shed light on the velocity differences/acceleration in stellar chromospheric and coronal eruptions.