Disclaimer: Nothing belongs to me, and before anyone can object "But they're brother and sister!"...it's canon, or at least, bordering on canon. Lelouch is practically OBSESSIVE over Nunnally; everything he does is for her sake, she is the first person to come to mind when Shirley asks if he has ever felt the type of romantic feelings where he would dedicate more time for her than anyone else, hell he even calls her his "reason for living" (hence, the title). Also...this is the royal family we're talking about, so yeah...
Although, I am a C.C. x Lelouch shipper at heart, lol (though I did also ship Shirley x Lelouch until...*sigh*). But you don't have to view this 50 Sentences deal as strictly romantic; you can view it as platonic sibling love if you like (hence, the reason it is categorized under both "romance" and "family").
When his mother sits him down in her noticeably large lap and tells him he'll be gaining a little brother or sister in a few months, the first thought he has about it is, I'd rather have a puppy.
But when her first word is "Wawoosh", he thinks having a little sister might be preferable over a puppy after all.
She has difficulty learning how to walk and stumbles, but when her brother comes into the room she forgets all her fears of falling down and runs right over to him.
Nunnally's eyes light up as Lelouch presents her with his birthday present: A bouquet of flowers from the garden where he had endured prickly thorns just for her, and has the band-aids all over his arms.
And he endures them once again, though is more careful from experience, for two roses to give to Nunnally when she has come down with a miserable cold, and there is a picture to show for it.
The nanny walks in on them playing 'doctor' and drags Lelouch away by the ear when all he was doing was getting out his stethoscope.
"Big sis Euphemia...which one of us will Lelouch marry?"
Unbeknowst to the two sisters, Lelouch overhears this question and ponders to himself about whether Euphemia or Nunnally would be more suitable as a bride when he grows up.
What Lelouch enjoys the most about the summer is racing Nunnally across the yard, seeing her laugh and smile as the wind beats against their faces and tosses their neatly done hair.
What Lelouch hates the most about the summer is coming across the sight of the two people he cared for the most to see each of them in one of two states: Dead, and scarred for life.
Although she cannot see or walk, she feels the touch of her brother's hand and hears him softly whispering, "Nunnally..."
Of all things in the world, she is the one thing to remain pure and innocent in his eyes.
Even when the rain keeps them indoors, her smile becomes his sun.
The games they play outdoors with Suzaku take an interesting turn when he makes an off-hand suggestion of pretending to marry them off.
Although he feels overwhelmed with having to move to a different home, he knows that of all things to change in his life, Nunnally will always be the one thing to remain constant.
He strokes her tear-stained cheeks as she sobs about her nightmare where Lelouch suddenly abandoned her, and he assures her he'll always be here.
Although he cannot quite bring himself to share his own dream about her the following morning, and turns red in the face when thinking about it, resolving to never again glimpse through one of Milly's "forbidden love" romance novels at school.
He smacks Milly over the head when she casually asks if it's still acceptable for Britannian royalty to be married off to their siblings.
One of the reasons he likes her new hairstyle is because sometimes, she'll let him brush her hair in the morning, and get the particularly tough knots out of her hair by running his fingers through her long, silky hair.
As the reality of his new power begins to sink in, he envisions a world with peace—a world where Nunnally can live in happiness.
He holds her hand, noticing how soft and smooth her skin feels, and considers for a fleeting moment, though he knows it may be wrong, to take that hand and kiss it.
But linking his pinky with hers in a friendly gesture will do for now.
Nunnally's first thought upon meeting C.C. is, "Why didn't Lelouch tell me he had a girlfriend?"
Nunnally is not entirely sure why, but hearing C.C. imply the idea of her and Lelouch getting married leaves her with an odd feeling that both burns and aches.
She doesn't tell him, lest her wish not come true, but she is hoping to build a thousand paper cranes to grant her wish to be able to see Lelouch's smile.
He is aware of his feelings for her, and knows that, no matter how much it hurts, he must pair her off with Suzaku, for he is certain she cannot feel the same and wants her to be happy.
After hearing that Nunnally has been kidnapped, Lelouch feels a true sense of despair and thinks back to all the times he could've put off his homework for just a few more minutes to read to her.
And when it happens again, he thinks about all that is dear to him now more than ever, realizing that above all else, Nunnally comes first.
Even without his memories of Nunnally, Lelouch can't help but feel there's something missing in his life.
Of all things Lelouch is outraged by his memories being erased, he is furious beyond words to forcibly be forgotten his reason for living.
And he especially can't forgive Rolo for trying to become that new reason.
She can't help but detect Lelouch's odd tone while speaking to him after becoming Viceroy, though it is nice when he blurts out that he loves her.
He wants to take it to bring back those carefree days before this entire mess began, back when his mother was alive, back when he knew nothing of Geass, and most of all, back when he and Nunnally were at their happiest.
As Shirley fervently explains the power of love, Lelouch realizes how strongly her sentiments echo his own for Nunnally, and thinks back to his attempts to suppress those feelings, realizing his attempts were all complete failures.
He can barely bring himself to get out of bed and dress himself as Zero, knowing he will never again hear her sweet voice in the morning.
He angrily explains the reason for Nunnally's smile—gratitude—however, he is unaware that her gratitude extended to not only having help from others, but also to having her brother by her side.
She doesn't want to believe what Schneizel is telling her, she wants to scream at him to stop lying to her, she wants to deny Lelouch would ever do any of that; until the evidence is played, and she breaks down in tears.
The only thing more shocking than the discovery that his sister is still alive is hearing her refer to him as an "enemy".
As Nunnally searches for the key on the ground, she struggles with all her might to open her eyes and see, and it isn't until she imagines what she will finally say when Lelouch arrives that she looks around and realizes she no longer lives in darkness.
Lelouch had nearly forgotten what colour her eyes were until she opened them for the first time in years, and noticed they were like lilacs.
She is angered to hear he has caused all this bloodshed for her sake and informs him she was happy with her brother by her side; she didn't want peace to be brought about this way, especially not if it would turn him into a monster.
It breaks his heart to have to use his Geass on her, but he knows it must be done in order to stop this.
It breaks him even further to turn a deaf ear to her cries after she falls to the ground, weak and helpless.
She dares not speak a word to him while in captivity, and he returns the favour, but all it takes for Lelouch to feel too ashamed to come back down to visit is to see the angry, defiant tears in her eyes.
Even now as she's in chains and dressed too thin for the winds on this day, she can never bring herself to hate her brother, and when she tries, she still remembers those summer days they spent laughing and playing.
And she realizes how much she truly loves him as she looks on in despair to see Zero thrust his sword right through her beloved brother.
Lelouch remembers hearing about people seeing a bright light before dying, and he supposes this must be true, for even though he feels a massive ache through his chest, the last sight he sees is his guiding light.
Even though she knows it's too late, she sobs out once again that all she needed was her brother, and begs for him to wake up, knowing he never will ever again, nor will he ever hear her declaration of her feelings for him.
Even though it is hard, she knows she must move on, for her brother wouldn't want to see her in such heartache...
A/N: So yeah, this was my first time with this sort of thing, so it's probably not too great (although it's probably a tad creepy for some, lol). I left the last one deliberately ambiguous, so make of it what you will.