  We outline some of the highlights of the scientific case for the advancement
of stellar high energy physics using the Line Emission Mapper X-ray Probe ({\it
LEM}). The key to advancements with LEM lie in its large effective area -- up
to 100 times that of the {\it Chandra} MEG -- and 1~eV spectral resolution. The
large effective area opens up for the first time the ability to study
time-dependent phenomena on their natural timescales at high resolution, such
as flares and coronal mass ejections, and also opens the sky to much fainter
targets than available to {\it Chandra} or {\it XMM-Newton}.
