Kono Danshi, Sekika ni Nayandemasu.

A high school student named Ayumu Banri suffers from a condition that causes him to crystallize when stressed. Struggling to connect with his classmates, he repeats a grade and decides to pursue a "Sparkly youth" by altering his appearance and keeping up with trends. As he navigates this new persona, his homeroom teacher and geology instructor, Kouya Onihara, comments on the aesthetic of Ayumu's transformation. Encouraged by this, Ayumu grows increasingly drawn to Kouya, who offers him guidance.