Takateru Akiyanagi is a student and Yumeji Fujiwara's close friend. Known among friends as "Taka," he carries the title "Master of Haiku." He habitually expresses his thoughts through spontaneously composed haikus, concluding each one with "...by Akiyanagi Takateru." This signature flourish punctuates both casual conversation and subtly ironic remarks, serving as his primary form of personal artistic expression.

His dedication to haiku began as a way to cheer his hospitalized sister, evolving from a meaningful ritual to make her laugh into his distinctive communicative style. Despite a quiet and melancholic demeanor, Takateru occasionally uses his haikus for lighthearted teasing, often directed at Yumeji. His reserved nature makes his true feelings or intentions difficult for others to discern, even for Saki Kirishima.

Takateru's role becomes pivotal when he is revealed as the vessel possessed by the dream demon Pharos Hercules. Hercules gradually consumes Takateru's mind and body, achieving complete control. This transformation occurs partly because Yumeji, respecting Takateru's discomfort, refrains from using his dream-predicting ability on his friend, inadvertently allowing Hercules the necessary time. The loss of Takateru to Hercules triggers a profound emotional crisis for Yumeji, who blames himself for failing to prevent the possession.