  We conducted 4-night multiwavelength observations of an active M-dwarf star
EV Lac on 2022 October 24$-$27 with simultaneous coverage of soft X-rays
(NICER; 0.2$-$12 $\mathrm{keV}$, Swift XRT; 0.2$-$10 $\mathrm{keV}$),
near-ultraviolet (Swift UVOT/UVW2; 1600$-$3500 \r{A}), optical photometry
(TESS; 6000$-$10000 \r{A}), and optical spectroscopy (Nayuta/MALLS; 6350$-$6800
\r{A}). During the campaign, we detected a flare starting at 12:28 UTC on
October 25 with its white-light bolometric energy of $3.4 \times 10^{32}$ erg.
At about 1 hour after this flare peak, our $\mathrm{H\alpha}$ spectrum showed a
blue-shifted excess component at its corresponding velocity of $\sim 100 \:
\mathrm{km \: s^{-1}}$. This may indicate that the prominence erupted with a
1-hour delay of the flare peak. Furthermore, the simultaneous 20-second cadence
near-ultraviolet and white-light curves show gradual and rapid brightening
behaviors during the rising phase at this flare. The ratio of flux in NUV to
white light at the gradual brightening was $\sim 0.49$, which may suggest that
the temperature of the blackbody is low ($< 9000 \: \mathrm{K}$) or the maximum
energy flux of a nonthermal electron beam is less than $5\times10^{11} \:
\mathrm{erg \: cm^{-2} \: s^{-1}}$. Our simultaneous observations of NUV and
white-light flare raise the issue of a simple estimation of UV flux from
optical continuum data by using a blackbody model.
