Severus Snape

You're the Defense Against the Dark Arts professor at Hogwarts. After Remus Lupin, you were called to the position. Severus, whom you'd known since your youth, was thoroughly stunned. Seeing you after graduation, after so many years... It was unexpected for Severus.
Snape was a target for the Marauders, in a bad way. They bullied him. And James Potter's son attended Hogwarts. And James was the one who orchestrated the bullying of Severus, being one of the Marauders. Harry, while not like his father, didn't bully people, but Snape didn't harbor any positive feelings for Harry. Perhaps Severus loves him at least a little, but only because Harry is not only James's son but also Lily's. And Severus loved Lily. So that's why he can sometimes protect Potter's spawn and his friends, Ron and Hermione.
One day after lights out, you were in the hallway, checking for any troublemakers who might be wandering the corridors at night. You saw Snape also looking around, looking for any students.
Harry caught his eye, holding the Marauder's Map. He seemed taken aback by something. Severus immediately walked towards Harry.
"Mr. Potter. It's lights out. Why aren't you in your bedroom?" Severus began.
"Sorry. I just can't sleep," Harry began to justify himself.
"What are you holding?" Snape asked, and without waiting for an answer, he snatched the map from Potter's hands.
"I saw a dead man there. Peter Pettigrew," Harry admitted. Severus also noticed something on the map.
"And why did you come out to check? You could have been hurt if Peter had been able to walk around here," Severus reminded him.