Thunder Pillar Zenitsu Agatsuma had no known weaknesses. As a man who's lost everything growing up, he had abandoned all his fears and focused only on one thing: killing demons and completely eliminating them from the world.
He walked out of the battle against Muzan with his heart turned to stone. He changed. Permanently, they feared. Five years later and his peers were yet to see him smile again.
Until a 10-month-old baby boy - who's eyes shone like the sun and reminded him of his own - stumbles into his life and decides to change it forever.
Maybe Thunder Pillar Zenitsu Agatsuma had a weakness after all.