The J-PARC Sterile Neutrino Search at J-PARC Spallation Neutron Source (JSNS^2) experiment has started in 2020. We took data with long physics run from 2021 to present and several analyses with the data are on-going. From the analyses, we found that the largest background is coming from fast neutrons induced by cosmic rays. In order to reduce the background, we dissolved diisopropyl-naphthalene (DIN) in the Gd-loaded liquid scintillator (GdLS) by 10% of weight and we started to develop an effective pulse shape discrimination (PSD) algorithm. The current PSD capability is as follows: the rejection power of fast neutron is more than 95 % while the signal efficiency is more than 90 %. In this presentation, details of hardware development, methodology of PSD and PSD capability will be described.