Snapes and bellas daughter

Prologue

Halloween, 1981
Sev walked to his ex's house and knocked 3 times.
"Oh hi Sev, hi Cassy, baby" lily cooed as she opened the door.
"Hello lily, thank you for looking after her" sev replied
"Of course anytime, anyway you don't want to be late" lily told him as she took Cassy out of his arms.
"Thank you again, lily" sev said before apparating to Malfoy manor.

"Severus, please come sit" Voldemorts raspy voice called as sev walked through the door, his cloak blowing behind him.
"I have wonderful news, I have found the potters location" with those last words Sev's heart dropped .
"I shall go and get the boy, tonight" at this point sev was praying that the meeting would end soon so he could go and get Cassy and warn lily.

The meeting slowly came to an end and Snape quickly apparated. As he landed, he fell to the floor with a throbbing, horrible pain in his arm. He noticed he had been splinched, he ran to the nearest fire place and flooed to his house.

He arrived home and quickly went to his study to grab a blood replenishing potion but before he could drink it, black spots covered his vision before he dropped to the floor, the glass shattering over his face. He woke up to a slight kick, as his eyes came into focus he saw Albus Dumbledore towering over him with a sad look on his normally sparkling eyes.
"Albus wh-" everything came rushing back to him, Albus watched as panic took over his ex-students eyes.
"Cassy, is she okay? Never mind she will be she was with lily" he rambled trying to reassure himself that nothing bad happened. He abruptly stood up and flooed to the potters.

The green flames disappeared as sev rushed around the house, the first thing he saw being his bully's body laying on the stairs dead. Sev ran up the stairs but stopped not knowing which way to go until he heard a cry from the room on his left, he ran in and almost tripped over something in his worry. He looked down and saw the love of his life, who's gorgeous eyes usually brightened up the his day, laid there lifeless, her red hair spread out around her. Sev fell to the floor cradling her head denying that she was dead until a baby's cry snapped him back to reality where he started searching for his daughter. He ran like a lunatic around the house looking for her, after a few hours he gave up and apparated to Albus to see if he knew where she was. He didn't.

That was the day 'Sev' turned into 'Snape'. He was distraught so he took it out on his students. Everyone hates him until....