  High-redshift ($z>2$) blazars are the most powerful members of the blazar
family. Yet, only a handful of them have both X-ray and $\gamma$-ray detection,
thereby making it difficult to characterize the energetics of the most luminous
jets. Here, we report, for the first time, the Fermi-Large Area Telescope
detection of the significant $\gamma$-ray emission from the high-redshift
blazar DA 193 ($z=2.363$). Its time-averaged $\gamma$-ray spectrum is soft
($\gamma$-ray photon index = $2.9\pm0.1$) and together with a relatively flat
hard X-ray spectrum (14$-$195 keV photon index = $1.5\pm0.4$), DA 193 presents
a case to study a typical high-redshift blazar with inverse Compton peak being
located at MeV energies. An intense GeV flare was observed from this object in
the first week of 2018 January, a phenomenon rarely observed from high-redshift
sources. What makes this event a rare one is the observation of an extremely
hard $\gamma$-ray spectrum (photon index = $1.7\pm0.2$), which is somewhat
unexpected since high-redshift blazars typically exhibit a steep falling
spectrum at GeV energies. The results of our multi-frequency campaign,
including both space- (Fermi, NuSTAR, and Swift) and ground-based (Steward and
Nordic Optical Telescope) observatories, are presented and this peculiar
$\gamma$-ray flare is studied within the framework of a single-zone leptonic
emission scenario.
