Sprouting Spring.museum. As a studious and resourceful boy, he attempts to find his way back. He finds a mysterious spirit-like girl but she disappears, and for some reason feels particularly nostalgic to him and is a presence unknown to the others. Meanwhile, the teenagers hold a meeting after noticing some strange happenings during the confrontation. Mikoto's barrier was broken despite her mental conditions and health being at peak levels, and there was no debris inside from the oncoming aircraft outside, meaning there had to be a traitor amongst them. Kakeru proposes a pair system where each person can keep watch over their own partner, pairing up with Koharu. Everyone else departs to carry out post-battle investigations and cleaning up. Mikoto and her partner Sakuya head to the library to conduct research, where she remembers their promise as childhood friends to forever love each other, but now that they've grown up she wishes to be more focused on duty. Koharu later finds out how Kakeru was abandoned by his father four years ago, with an ear cuff as the last thing to remember him by.