Matsuri Kazamaki and Suzu Kanade were close friends as children due to their shared ability to see ayakashi-youkai that search for life force to consume. However, their relationship deteriorated in high school as Suzu's feelings for Matsumi grew stronger, while Matsumi viewed all ayakashi as threats. They encountered a talking white cat named Shirogane, who was actually a four-hundred-year-old ayakashi known as the "King of Ayakashi." Shirogane aimed to gain more power by consuming Suzu, but Matsumi tried to save her by sealing his powers. As a result, Shirogane used a jutsu to transform Matsumi into a girl. Matsumi vowed to protect Suzu as her best friend while she learned how to act like a girl until her grandfather-a renowned wind jutsu exorcist ninja-could reverse the jutsu. Meanwhile, Suzu had to deal with her romantic feelings for Matsumi now that he was no longer a boy. However, things took a turn when Matsumi took Shirogane as his pet, leaving their friendship uncertain.
Ayakashi Triangle was simulpub in English through MANGA Plus. The first 2 volumes of the series were published digitally in English by VIZ Media from July 27, 2021 to October 26, 2021, and republished in print by Seven Seas Entertainment under the Ghost Ship imprint since November 1, 2022.