Ayumu Tamari lives with "Crystallization Syndrome," a condition where extreme stress causes parts of his body to turn into crystals, severely limiting his movement. His intense social anxiety makes it nearly impossible to talk to his classmates, triggering frequent crystallization episodes and forcing him to repeat a year of high school. The only person who brings him comfort is his homeroom teacher, Kouya Onihara—whom Ayumu fondly calls "Oni-chan Sensei." Kouya, a devoted crystal enthusiast and researcher, is captivated by the unique formations that appear on Ayumu's body. As Ayumu navigates the pressures of school life and the complicated feelings in their forbidden relationship, he works to find a sense of normalcy and learn to control his emotions before he becomes completely crystallized.
