The KL —> pi0 nu nu-bar decay is one of the sensitive probes to search for new physics beyond the Standard Model. Because the branching ratio predicted by the Standard Model (3 x 10^{-11}) and its theoretical uncertainty are small, a small deviation from the prediction would signify an existence of new physics. Although the decay mode is theoretically clean, it is difficult to observe experimentally. Not only because the observable particles are limited to two photons from the pi0, backgrounds should be controlled and understood to the level of O(10^-{11}). In this talk, I will briefly review several experimental ideas in the past, explain how the current J-PARC KOTO experiment started and progressed, and show some future plans.