Following the triumph of I Hear the Sunspot, its sequel, I Hear the Sunspot: Theory of Happiness, delves into the evolving dynamic between two individuals straddling the delicate line between friendship and romance. Kohei, grappling with a hearing impairment that isolates him, finds solace in the company of the spirited and extroverted Taichi. Initially reticent, Kohei gradually sheds his barriers as he grows closer to Taichi, fostering a heartfelt connection that transcends mere companionship.