  Massive stars play critical roles for the reionization of the Universe.
Individual massive stars at the reionization epoch (z > 6) are too faint to
observe and quantify their contributions to reionization. Some massive stars,
however, explode as superluminous supernovae (SLSNe) or pair-instability
supernovae (PISNe) that are luminous enough to observe even at z > 6 and allow
for the direct characterization of massive star properties at the reionization
epoch. In addition, hypothetical long-sought-after PISNe are expected to be
present preferentially at high redshifts, and their discovery will have a
tremendous impact on our understanding of massive star evolution and the
formation of stellar mass black holes. The near-infrared Wide Field Instrument
on Nancy Grace Roman Space Telescope will excel at discovering such rare
high-redshift supernovae. In this work, we investigate the best survey strategy
to discover and identify SLSNe and PISNe at z > 6 with Roman. We show that the
combination of the F158 and F213 filters can clearly separate both SLSNe and
PISNe at z > 6 from nearby supernovae through their colors and magnitudes. The
limiting magnitudes are required to be 27.0 mag and 26.5 mag in the F158 and
F213 filters, respectively, to identify supernovae at z > 6. If we conduct a 10
deg2 transient survey with these limiting magnitudes for 5 years with a cadence
of one year, we expect to discover 22.5 +- 2.8 PISNe and 3.1 +- 0.3 SLSNe at z
> 6, depending on the cosmic star-formation history. The same survey is
estimated to discover 76.1 +- 8.2 PISNe and 9.1 +- 0.9 SLSNe at 5 < z < 6. Such
a supernova survey requires the total observational time of approximately 525
hours in 5 years. The legacy data acquired with the survey will also be
beneficial for many different science cases including the study of
high-redshift galaxies.

High Energy Astrophysical Phenomena;Cosmology and Nongalactic Astrophysics;Astrophysics of Galaxies;Solar and Stellar Astrophysics