Bring a large pot of salted water to a boil. Add the spaghetti and cook until al dente, stirring often, 8 to 10 minutes. Drain well, reserving 2 cups of the pasta water.
Heat a large skillet over medium heat. Add the olive oil, garlic and Thai chile, and cook until softened and fragrant, 2 minutes. Add the edamame, scallions, butter and salt; cook for an additional minute, until the edamame is heated through and the scallions are soft. Add the drained pasta and the shiso, sesame seeds and the reserved pasta water. Simmer for about 1 minute, tossing gently, until the sauce is creamy. Serve topped with a small dollop of tobiko.