KOTO is searching for New Physics through the $K_L^0\to\pi^0\nu\overline{\nu}$ decay. We report the two major backgrounds of $K_L^0 \to \pi^0 \nu \overline{\nu}$ search at KOTO: $K_L^0$ and $K^+$ produced at the collimator. In order to suppress them, an in-beam veto counter has been installed at the KOTO detector entrance to detect $K^{+}$ particles. Also, an algorithm connecting the cluster shape with the reconstructed incident angle has been developed to suppress the beam halo $K_L^0$ decays. With those tools, KOTO is prepared to explore the sensitivity of $O(10^{-10})$. We also search for the ${K_L^0\to\pi^0 X}$ decay, where $X$ is a hypothetical invisible particle, and set $BR(K_L^0 \to \pi^0 X, M_{X} \approx M_{\pi^0}) < 3.7 \times 10^{-9}$ (90\% C.L.) (preliminary).