Astral is contacted by Kei Isurugi, a member of the school of Onmyōdō that Nekoyashiki once attended, to perform a ceremony at a mountain. Itsuki accompanies Nekoyashiki and Mikan, but they are attacked by Kei during the ceremony. Kei remarks that he lost his sister, Sakuya Isurugi during a similar ceremony three years prior because Nekoyashiki left the school at the time to take Mikan to Astral. Nekoyashiki challenges Kei to a personal duel, and Itsuki upholds this, stopping the arriving Honami and Adilisia from interfering. Despite Kei's use of kuda-gitsune, Nekoyashiki manages to defeat him, with Kei pleased that he was able to pose some level of challenge for Nekoyashiki, his idol at the school. As Kei lies in defeat, Nekoyashiki reminisces on his last experience with Sakuya as the group watches an aurora in the sky.