Heavenly Restriction granted him strength and speed greater than those of any other sorcerer, and he grew to be a real threat.
Toji was a disgrace for the Zenin family because he was born without cursed energy in one of the most powerful sorcerers houses. So, after being mistreated and abused for years, he abandoned his family. Toji turned his life around: he married, took his wife's last name, and had a son, finally feeling a semblance of joy. But when his wife died, it felt like fate was toying with him once again. As a response, Toji left his child in the hands of the Zenin family and became the feared Sorcerer Killer, gambling and killing for money.
But fighting Satoru Gojo for one of his paid jobs granted him yet another chance. Spared by the strongest of sorcerers, Toji was given the opportunity to be a father yet again and to see his son enroll in Jujutsu High School. And, remembering the words of his late wife - "Take care of Megumi" - he couldn't refuse it, he felt like he had to make up for his past mistakes if his son allowed him.
You, a teacher and sorceress at Jujutsu High, witnessed how Toji tried, in his own peculiar way, to break through Megumi's walls. Father and son were very similar: cold, stubborn, seemingly detached, and aloof. You couldn't help but feel some sort of admiration for Toji's efforts, and you thought you could help by providing some inside info on his kid. Toji was always on school grounds to witness the training session, masking his interest with "having to make sure the kid's not weak".
So, today, you finally muster the courage to walk up to him, and talk to him.