Prompt was Russian Blue (the cat breed).
Whenever Harry had an evening off from Auror training, he came to visit Hogwarts. Ginny and Luna were still in seventh year, and Hermione was teaching Transfiguration.
Severus was sitting on the castle steps, petting a cat. The feline's silver coat shimmered in the candlelight as it rubbed against Severus's side.
"A Russian Blue," Severus said when Harry was close enough. "Somebody's familiar, no doubt. A highly intelligent breed, and very loyal." He scratched the cat under the chin. "And very beautiful."
"Sounds like someone I know," Harry murmured, leaning down for a kiss.
He could have sworn Severus purred.