  We present deep Keck/MOSFIRE near-infrared spectroscopy of a strong Lyman
alpha emitting source at z=6.1292, HSC J142331.71-001809.1, which was
discovered by the SHELLQS program from imaging data of the Subaru Hyper
Suprime-Cam (HSC) survey. This source is one of five objects that show
unresolved (<230 km s-1) and prominent (>10^44 erg s-1) Lyman alpha emission
lines at absolute 1450 angstrom continuum magnitudes of M1450~-22 mag. Its
rest-frame Lyman alpha equivalent width (EW) is 370+/-30 angstrom. In the 2
hour Keck/MOSFIRE spectrum in Y band, the high-ionization CIV 1548,1550 doublet
emission line was clearly detected with FWHM =120+/-20 km s-1 and a total
rest-frame EW of 37-5+6 angstrom. We also report the detection of weak
continuum emission, and the tentative detection of OIII] 1661,1666 in the 4
hour J band spectrum. Judging from the UV magnitude, line widths, luminosities,
and EWs of Lyman alpha and CIV, we suggest that this source is a
reionization-era analog of classical type-II AGNs, although there is a
possibility that it represents a new population of AGN/galaxy composite objects
in the early universe. We compare the properties of J1423-0018 to
intermediate-redshift type-II AGNs and CIV emitters seen in z=6-7 galaxy
samples. Further observations of other metal emission lines in the rest-frame
UV or optical, and X-ray follow-up observations of the z=6-7 narrow-line
quasars are needed for more robust diagnostics and to determine their nature.
