Death.
His mother committed suicide over his curse. He was too young then to save her.
He watched as Kyoko Honda got hit by a car. In front of him. Covered in blood. He could have saved her, but instead he let death take her. His curse had stopped him from pulling her to safety and saving her.
Finding Tohru on the ground, he felt as if his heart was breaking. He couldn't stop the tears as he begged Tohru not to die.
He wished there was a way he was sure to stop death from taking her from him.