Head cannons

alena black

Helena Violet Potter twin sister of Harry Potter
Remus is her godfather but felt like he couldn't raise her at all as he's a werewolf
Voldemort didn't attack and kill their parents until they were 4 ( he had a hard time finding them as they were constantly changing where they were living every few days until their parents decided to settle down)
James was holding Helena as he checked the door and was killed
Remus owled Sirius (they still had a great
relationship and told each other everything)
Sirius with the ok from Remus owled his brother Regulus black (they still had a great
relationship and Sirius explained everything to his brother and Regulus was a spy for Dumbledore ) and asked him to take Helena and help keep her safe Harry still lived with the Dursleys for the protection spell Lilly put on them
Regulus said yes
She calls him uncle Reg
Helena uses a fake name and backstory so no one except for very few people know she's a potter
Se goes by Alena Black
Her fake backstory is that she's the daughter of Sirius and his wife died shortly after Sirius was taken to Azkaban and Regulus took her in
She knows her real backstory too and she's seen pictures of her parents
She immediately recognizes Harry
Harry doesn't believe he has a sister until she turns around and shows him the scar she has and shows him a newspaper clipping from the day after their parents were killed
It reads the potter twins Helena and Harry 4 killed the dark lord Hogwarts headmaster Dumbledore says the twins are safe but where are they
The twins have matching lightning bolt scars Harry on his head and Helena on the back of her neck
Harry can't believe he has a twin sister