Sorrowful flash 悲しき閃光 is the 2nd episode in the 1st OVA.
The woman who rescued Tamahome introduces herself as "Kaen", who looks like Taiitsukun in her true form. Kaen tells Tamahome that when Tamahome defeated Nakago, Nakago didn't die but went into a deep sleep. When Nakago was revived, Nakago conquered his body, and Tamahome's soul went into Nakago's body, thus the two souls exchanged. Confused, Tamahome can't believe he is really Nakago. Kaen offers Tamahome a bowl of sake to help him calm down and relax, which he drinks. After he falls asleep, Kaen undresses and offers to use Soi's celestial ability to raise his chi through coupling with him. Tamahome tells her to go away, and leave him alone.
Later, Tamahome fights with Kouji, the leader of the Tasuki's former band of bandits, who also sees Tamahome as Nakago who destroyed Mt. Reikaku in the war beteween Konan and Kutou. During the battle, Tamahome unleashes Nakago's blue chi attack killing many of the bandits and fatally wounding Kouji. Kouji tells Tamahome that only a year has passed since the summoning, then pulls out a bomb saying he will bring Tamahome back. As the blast hides and covers them, Kaen changes into Tomo and reveals the sake Tamahome drank was full of Kodoku, the drug that once caused Tamahome to almost kill Miaka.
Nakago says anything he sees since he arrived in Konan was an illusion made by Tomo, but the Kodoku in the sake was real. In the real world, the group have approved that all of the priestesses will disappear and that Takiko (the priestess of Genbu )'s existence is slowly being erased. Yui goes into a dream and is pulled into The Universe of the Four gods . Meanwhile, Chichiri, who felt Tamahome's chi, and Tasuki meet with Suboshi, who is using his brother Amiboshi's body. Tomo arrives with Yui, who now becomes the Priestess of Genbu, and two children who are her first Genbu warriors. Nakago/Tamahome also appears. Realizig Yui was the one who stole the book, Miaka goes into the book to go after her.