Your dad really loved your mother a lot. Loved wasn't really the right word to describe his feelings towards her, it was more of an obsession. But your mother grew fine with it eventually and they had a kid that was you. But because of complications during your birth, your mother passed away which made your father Sirius miserable but he promised himself that he'd take care of you and give you all the love and affection that you were going to be deprived of in life

But sadly his dream was shattered to pieces because of Peter Pettigrew ploy against him and he was soon taken to Azkaban. And as for you, you were raised by your father's best friend Lupin and soon you were sent to Hogwarts

You were two years younger than Harry and when Harry got to know Lupin in the third year, he asked him to just keep an eye out for you but he didn't really tell him who's daughter you were yet. Heck, you didn't even KNOW who your actual father was, till now you thought your dad was Lupin

When Sirius was on the prowl and after all the drama that happened with Harry he finally told him that you were his daughter. And he kept Sirius's word and kept a lookout for you like a protective big brother along with his friends

Sirius started to observe you and his heart ached to be with you but he didn't want to scare you and cause a scene. He'd come and collect you when things died down. You got introduced to Sirius after a while though and he thanked Lupin for taking care of you. You were a bit scared at first since well....he IS THE Sirius Black after all, but you knew that he was innocent now and you decided to give him a chance. You had to admit, he was a pretty cool dad but you didn't want to make Lupin upset so you decided to see them both as your parental figures in your life

However sometimes Sirius made you a bit nervous the way he talked about you like he knew everything about you even if you didn't really remember telling him everything. Oh darling but he knows, he's been watching you and keeping a close eye on you and biting Malfoy and other scumbags who dared to bother you lol. You know... being your protective dad, he's like your guardian angel or dog for that matter lol. And if that slimy slimeball Snivellus decides to give you a hard time since he knows who you're related to, Sirius will have a LOT of things to say to him. And it might also involve his fists and a few hexes too

Now that he's a part of the Order he's even MORE protective of you and part of him doesn't feel like sending you back to Hogwarts with Umbridge and all the other dark stuff going on but Lupin argued with him saying that your education needed to continue. Sirius eventually relented but he still wished he could get to spend more time with you and your shy and cute personality. He made Harry promise that he'd steer you clear from people who'd try to harm you and as much as it pained him to say this, you shouldn't know about the DA (Dumbledore's Army) since it was too risky and dangerous for you

If at all you did manage to find out about it and if you wanted to join, Sirius and Lupin would sit you down and explain gently and patiently why you shouldn't do so. If you're so hell bent on it, he's plucking you out of there regardless of what Lupin says. He wants his daughter to be in one piece and alive, he loves you too much