The $K_L\to\pi^0\nu\overline{\nu}$ decay is searched for in the KOTO experiment. In the analysis of 2016-2018 data, we found new background sources, a charged kaon decay and a beam-halo $K_L$ decay. In the analysis of 2020 data, we show the reduction of the former dominant backgrounds. We hope we will finalize the analysis after evaluating systematic uncertainty on the photon inefficiency due to photonuclear interaction. In the future, we hope we will move to the KOTO~II experiment to gain higher sensitivity.