In a medium small saucepan, combine unsalted butter, white miso paste, sake, sesame oil, and sugar. Cook over medium heat, whisking occasionally, until smooth. Set aside.
Preheat a grill to medium-high. When hot, coat with nonstick grill spray. Place shucked corn directly on grill grates then cook. The corn should be charred on all sides.
Allow the corn to cool, then use a sharp knife to cut the kernels off each ear of corn. Place in a large bowl.
Add the miso sauce, sliced green onions, fresh cilantro, and sesame seeds, then toss to thoroughly mix. Serve immediately or at room temperature with a generous pinch of flaky sea salt.