Break Down the Walls (Divergent Story)

A\N: Okay, so this is my second major fanfic! Yay! So I found this idea on fanfiction.net and I kept the idea of Tobias having a younger sister, nothing else. You can go check it out, it's called 'Younger Sister' and it's set as the same initiation year as Tris, so basically it's all the main dialogue straight from the book. I didn't want to do that because that would be long, and a major hassle, so this character's choosing ceremony is set one year after Tris's. Basically, the war didn't happen. Tris and Four are together. Four has a younger sister. I hope you guys like it, because I enjoy writing it. I've got the initial story line planned out, so let's get this show on the road!
Prologue/Chapter 1

Life in Abnegation is supposed to be quiet. It's supposed to be peaceful and devoted to helping others. That's the nice side of Abnegation. That's the part that makes me shameful for wanting to leave.

But then there's the other half, the one that I encounter almost everyday no matter what-my father, Marcus Eaton. He is the leader of our faction, and I have figured out that there are two sides to him: there's the kind, quiet, loyal side, that makes me appreciate him.

But that only lasts for a second.

The other side is rougher, harder, monstrous even, it is the one that makes me want to flee from my family, that makes me cry myself to sleep every night.

But I have my brother. And my brother has me. That's how we survive in this house hold. We survive with each other.
We had our mother at some point in our lives, but she died before I was able to acknowledge how important she really was for me. I remember attending her funeral and the tears squeezing out of my eyes, clenching my brother's hand for dear life.

The door slams shut with a soft thud. Today is the day that my brother has to take his aptitude test, and tomorrow he will decide where he belongs. To stay here, or to leave us. Not us-I don't tend to associate Marcus and I as an us-but mainly me. He might choose to leave me. Marcus is now home, and I'm shaking-my hands, my toes, my legs-Tobias isn't home yet. Not that I need him to protect me, but he's always there in case things get out of hand.

Like, really out of hand.

"Catherine!" Marcus calls. I set my pencil down on my desk and close up my math book, telling myself my homework can wait for later.
"Coming, father." I say in a hushed voice. Shouting brings too much unnecessary attention to yourself. I descend the stairs as quickly and swiftly as possible, trying not to make a sound.
"Yes, father?" I ask in a small voice, bowing my head. He scans me up and down and sets his hand on his chin.
"Where is your brother?" he demands, running his fingers against the stubble that spreads across his lower cheeks.
"He had aptitude tests today. He will be coming home late," I say, wincing. Aptitude tests are during lunch. Tobias must be wandering about, somewhere in the streets, not taking into account the time, like he always does, that little shit, and the consequences that come when you're not here on time. 
"Are you lying to me?" he interrogates, leaning closer to me as if to speculate and study my face. My breaths are shaky yet strong once his face is only an inch away from mine.
"No," I stammer, unconvincingly. That's the thing about Marcus. He sees through all of my lies.
"I think you're lying to me!" the blow comes before the sentence ends and I am immediately thrown to the ground from its force. Marcus may be dwindling on the age side, but he packs a good punch. I touch my fingertips to the recipient end of the punch, and it feels swollen already. My eye starts to seal shut, and I know that I'm going to get a black eye. It's easy to cover up these kinds of things. Really, I just tell people I tripped. I just say, clumsy old me, tripped over my own legs. They're kind of long already, so people can actually try to believe it. With Tobias it's harder. But that's okay; Marcus is smart enough to know where to hit with him.
I stand up as quickly as possible, to not show weakness.
"What do I tell people at the choosing ceremony tomorrow? Some people are starting to doubt my excuses," I whisper.
He brusquely grabs me by the shoulders and says, "You tell them you fell. You tripped, and fell badly down the stairs." He pulls back.
"Do you understand me?" he demands. I nod my head. "Now go on. I have people coming over." I nod and walk back upstairs. To the washroom I go, wetting a washcloth until it's damp. I dab it to my eye which is becoming a deep shade of blue-purple already, and wince. It's very sensitive. But I'm used to the pain. After a while, I barely feel it. I wander back to my bedroom and open my math book. The numbers and explanations make my head spin. I slam the book shut, letting out a frustrated sigh, just as the front door opens again. Tobias is home.
"Hello father," he greets Marcus, then walks upstairs with his bag slung across his shoulder.
"Get back here, young man." He calls. Tobias turns around and goes to speak with father and I close my door until I can only see a slit of outside. Eavesdropping is a selfish act. And committing selfish acts in this house is worth a beating. I open up a different textbook, my faction history one. In it, it teaches each faction and their manifestos.
Amity believe in kindness, something that deeply interests me. I love being kind, projecting outwards. I love the idea of being kind, but I'm not. I have a temper. I like annoying people. Amity wouldn't be right for me. I couldn't fit in.
Candor always speak their minds and tell the truth, something that has always been a struggle for me. I always lie, to Tobias, to father, to the people around me. It's better that I keep myself guarded as much as possible, or else I'll let people in. I can't let people in. They wouldn't like me. When I put up walls, they never crumble.
Next is Erudite. They believe that knowledge is the key. I do believe that we must be educated, and that we must know about our world. But I don't believe that we should have knowledge at all costs. People at school said that they test serums and medicine on rats and mice and such. I don't think we should harm innocent animals to learn about something like that. I mean, how would it feel to be poked and prodded? Not so good.
Dauntless. The brave. I always watch them in the mornings, going into school, how they gracefully jump off the trains. I always think to myself, maybe I could be like them one day, but I never believe that I could have neither the bravery nor the inner strength to do something like that. The idea of becoming like them and choosing to be with them is always at the back of my mind, but could I really do it?
And finally, Abnegation. I believe in selflessness, in forgetting myself and helping others, because it makes me feel good inside that I helped someone. That I made someone's day even better. I believe that I could belong amongst the quiet, gray-clothed people that I see in my quotidian life, but there's one issue to staying here: Marcus. I wouldn't be able to move out until I'm eighteen. That's the age you get to pick a house; that's the age you get to start picking a spouse. That would mean to spend two extra years with a monster, and I'm not sure if I could do that. Not with the way he treats us.