The J-PARC MLF neutron target is suitable as an intense neutrino beam from $\mu$ decay at rest ($\mu$DAR) for the sterile neutrino. Pure $\bar{\nu}_{\mu}$ beam can be available thanks to the low duty factor of beam spill and 1 MW proton beam power of the MLF. Estimation of the pion production rate is one of the significant challenges in the sterile neutrino search. And therefore, several MC simulations are carried out to understand the uncertainty. In addition to the sterile search, neutrino from kaon decay at rest ($K$DAR) is also an interesting channel to probe neutrino interaction with monogenic energy. The environmental background related to the proton beam was measured using a plastic scintillator detector. Finally, we confirmed that there is almost no environmental background expected for the sterile neutrino search at a distance of 20 m behind the mercury target.