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We report the identification of an unusual absorption line system in thequasar SDSS J080248.18$+$551328.9 and present a detailed study of the system,incorporating follow-up optical and NIR spectroscopy. A few tens of absorptionlines are detected, including He I*, Fe II* and Ni II* that arise frommetastable or excited levels, as well as resonant lines in Mg I, Mg II, Fe II,Mn II, and Ca II. All of the isolated absorption lines show the same profile ofwidth $\Delta v\sim 1,500$km s$^{-1}$ centered at a common redshift as that ofthe quasar emission lines, such as [O II], [S II], and hydrogen Paschen andBalmer series. With narrow Balmer lines, strong optical Fe II multiplets, andweak [O III] doublets, its emission line spectrum is typical for that of anarrow-line Seyfert 1 galaxy (NLS1). We have derived reliable measurements ofthe gas-phase column densities of the absorbing ions/levels. Photoionizationmodeling indicates that the absorber has a density of $n_{\rm H} \sim(1.0-2.5)\times 10^5~ {\rm cm}^{-3}$ and a column density of $N_{\rm H} \sim(1.0-3.2)\times 10^{21} \sim {\rm cm}^{-2}$, and is located at $R\sim100-250$pc from the central super-massive black hole. The location of the absorber, thesymmetric profile of the absorption lines, and the coincidence of theabsorption and emission line centroid jointly suggest that the absorption gasis originated from the host galaxy and is plausibly accelerated by stellarprocesses, such as stellar winds \zhy{and/or} supernova explosions. Theimplications for the detection of such a peculiar absorption line system in anNLS1 are discussed in the context of co-evolution between super-massive blackhole growth and host galaxy build-up.

Unshifted Metastable He I* Mini-Broad Absorption Line System in the Narrow Line Type 1 Quasar SDSS J080248.18$+$551328.9