Smaller dark matter subhalos are more abundant in the Milky Way. The survivability of such subhalos in the Milky Way depends on their structure. This suggests that the structure of subhalos can determine the fine structure of the Milky Way halo. I report the results of high resolution cosmological simulations of very small scale structure formation peformed on K computer. I focus on the formation and evolution of dark matter halos near the free streaming scale, and their impact on the indirect dark matter detection experiments.