Aki Suzumiya (Anne), a detective from the First Investigation Division, arrives at a riverbank with her partner, Takagi (Gaku Hamada), to examine a suspicious corpse. The body has been completely drained of blood, marked with a strange brand, and left holding a flower that symbolizes "love." Around the same time, a body is discovered in Finland, killed using the exact same modus operandi. Defying her superiors, Aki travels to Finland on her own. There, she begins an investigation alongside Jon Laine (Jasper Pääkkönen) of the Finnish National Bureau of Investigation—but what awaits them?

After being attacked by an unknown assailant at her hotel, Aki ends up staying at Yong's place. She begins an investigation alongside Yong and Katrina (Alina Tomnikov), but they fail to uncover any significant leads. Meanwhile, back in Japan, Aki's younger brother, Ryuji Suzumiya (Mahiro Takasugi), is placed in charge of the case—a decision made by their father, Tokuro Suzumiya (Jun Kunimura). Amidst this, Aki realizes that the date of the murder and the brand mark found on the victim's body hold a crucial, deeper meaning. When the brand is analyzed, a strange pattern emerges…

With the help of Zetter (Zefan Smith-Gnaist)—a German genius hacker and acquaintance of Yon—Aki discovers that the patterns in question bear a striking resemblance to those seen at Japanese festivals. Aki and Yon return to Japan to conduct further investigations; guided by Kitajima (Kanji Furutachi), the deputy chief of the Kayama Police Station, they visit the shrine where the festival takes place—and there, they finally uncover a connection to Finland. Furthermore, they realize that the victims, who initially appeared to have no relation to one another, actually share a significant commonality...