The KOTO experiment at J-PARC searches for the rare decay, $K_L \rightarrow \pi^0\nu\overline{\nu}$. The mode is CP-violating, with a theoretical branching ratio highly suppressed in the Standard Model at $(2.94 \pm 0.15) \times 10^{-11}$. With a small theoretical uncertainty, this search is sensitive to new physics. In the analysis of 2016-2018 data, three events were observed within the signal region, which was consistent with the background estimation. An upper limit on the branching ratio was set at $< 4.9 \times 10^{-9}$ (90% CL). Since that analysis, new hardware and analysis methods have been implemented to reduce the background level significantly. The search in 2021 had a single event sensitivity of $9.26 \times 10^{-10}$ which was comparable to 2016-2018 data taking. No events were observed in the signal region, which allowed KOTO to set the best upper limit on $BR(K_L \rightarrow \pi^0\nu\overline{\nu})$ to date at $< 2.1 \times 10^{-9}$ (90% CL). This is a report on the latest result of the search from data taken in 2021.