My version of how this happened. Hermione is a death eater but secretly is on the Orders side. No one knows she is a death eater except a small group of Slytherins.
"Who is that? Neville, who is that?" Ginny asked as she and the Hogwartians made their way to their half of the courtyard and saw something in Hagrid's arms.
"I... I don't know Gin. It looks like... No!" Neville gasped.
He was standing at the very front with Ginny and Hermione and Luna. Ron had died at the hands of Voldemort himself after being captured, refusing to give any information and somehow being able to use occlumency without any practice.
"Harry Potter, is dead!" Voldemort called out.
Ginny screamed and tried to run forwards, but Neville wrapped his arms around her waist and held her back so she wouldn't die.
"Silly girl," Voldemort chuckled, "He died trying to save himself. He died escaping and leaving you all behind."
"Liar! Harry wouldn't do that!" Hermione screamed with a discreet wink at Voldemort, pretending to show she was only acting although she felt every bit of anger she had acted.
"Ah, Miss Granger," Voldemort said, "On the contrary he did. And now I will rule over the wizarding world. From now on, you put your faith in me. Come over and declare yourselves or die."
No one moved, no one breathed until Lucius spoke up. He was also a spy for the order although he didn't give information but destroyed from within along with Narcissa, Draco, and Hermione.
"Draco," he called out.
Draco came forward and stood next to Hermione. He gave a sideways glance at her and she nodded slightly. He took a deep breath and crossed the field to Voldemort.
"Draco, very good," Voldemort said with an awkward hug before sending Draco off to his parents.
"I have won," he said again this time looking directly at Hermione, "So you may now come."
Hermione took a deep breath and slightly squeezed Neville's hand that she had been holding hoping to get a message across to him. Neville seemed to understand because his eyes widened for half a second before he dropped Hermione's hand.
Hermione took a deep breath before she took a single step forward.
"No!" Ginny gasped as Hermione started walking to Voldemort, "No! Hermione! You lied to us!" She screeched.
"Ginny," Hermione said.
"No," Voldemort said, "No use trying to make them understand. They will all die."
"Yes my lord," Hermione said before walking up and standing next to him where he had pointed her too and facing the Hogwarts crowd.
"Your very own war hero is mine," he snarled, "Hermione. Kill one of them."
Hermione nodded and walked forward a bit raising her wand. The Hogwarts side all gasped again and many screamed at her with foul comments but Voldemort silenced them. Hermione pointed her wand directly at Neville and stared him in the eye, 'play along' she mouthed.
Neville nodded and raised his hands in surrender. He gave Luna his wand before stepping forward and walking towards Hermione.
"Him?" Voldemort asked almost mockingly.
"Yes," Hermione sneered, "If he doesn't die first he will surely cause a rebellion and these filthy blood traitors trust him the most after me. Well they used to trust me. After him its those girls. I'll deal with them later."
"Very good, kill him." Voldemort said smiling at his daughter.
"One thing first, dad," Hermione said she whipped around and pointed her wand at Voldemort while Neville took out his spare and did the same, "You die first."
"Hermione?" Voldemort asked, "I should be guessed. You have your mother's heart."
"Do not speak of my mother," Hermione growled.
Voldemort flicked his wand and sent a spell at Neville who blocked it. He sent spell after spell at him but even with the help of Hermione, was blasted off his feet and hurled towards the Hogwarts side where Seamus and Dean managed to catch him with the help of George and Bill.
"Hermione. Join me or die," Voldemort said disarming her with ease.
"Die," Hermione declared.
Voldemort laughed and raised his wand at her, "AVADA KED--"
"I dare you to finish that spell," Draco growled raising his wand to Voldemort, his parents following.
"Draco," Voldemort sneered with disgust, "Don't tell me you've fallen for her."
"More than you could even imagine," Draco said and Hermione whipped her head to him for a moment ins hock before looking back to Voldemort, noticing Harry moving slightly and smirking.
"Then you will both die, along with you Narcissa, Lucius. I expected better from you," Voldemort said.
"You've forgotten something," Hermione said using wandless magic to get into Draco's mind and tell him Harry was alive but needed a wand, "Seven. Your snake is dead. She was six. But what's seven?"
"There is no seven," Voldemort snarled, "But no matter. I shall make a seventh."
"That's where your wrong. You see when you cast the killing curse on Harry for the first time, his mother had cast her love between you two. The curse rebounded on yourself and you killed yourself. Your soul was split yet again by mistake and latched itself on the only living thing it could find."
"No," Voldemort gasped.
"Oh yes," Hermione smiled before screaming, "DRACO NOW!"
Draco sprinted around Voldemort as Harry rolled out of Hagrid's arms. He threw Harry the wand before grabbing Hermione and pulling her out of the way of the two colliding spells.
"Fight!" Voldemort screamed.
"Everyone, Great Hall," Hermione yelled as the students and teachers ran into the castle, "Were better together."
The battle raged inside the Great Hall, seemingly never ending. Hermione and Draco stuck together, back to back, the entire time. Their skills combined were almost as great as Voldemort's, possibly better. The death eaters were no match for them.
Soon Harry had cornered Voldemort. After a grand speech between the two they both shot out their curses. Voldemort's wand shattered at the impact and he died.
"We won," Hermione breathed with a grin as she a Draco approached the group of hero's consisting of Harry, Ginny, Neville, and Luna.
"We did," Harry said hugging her tightly before putting his hands on his hips with a stern look, "But you're Voldemort's daughter? And you never told me?"
"I didn't exactly plan on being his daughter," Hermione said rolling her eyes as Blaise and Pansy joined them, hugging her and Draco tightly, "Only they knew. And Draco's parents. We've been sabotaging his plans from the inside since we all made it to his inner circle."
"Alright. But how did Neville know?" Ginny asked.
"Simple," Neville shrugged, "She squeezed my hand and that was obvious she was the death eater, but her posture was definatley angry. Sh wasn't a true follower and I understood so she choose me to potentially kill since I'd fight with her."
"H-How did you do that?" Hermione asked astonished.
"Hang around Luna long enough and you pick up a thing or two," Neville smiled wrapping am arm around Luna's waist as she smiled up at him.
Hermione and Ginny shared a look before squealing, "Nuna!"
"I'm not going to ask," Harry said rolling his eyes before he realized something, "Wait where's Ron?"
"Harry," Hermione whispered, the mood suddenly going dark, "He died."
"No," Harry said firmly, "Its not good to lie Hermione. I already said that. Where is he?"
"Harry," Ginny said tears falling, "H-H-He's r-really g-gone. Voldemort killed him when he wouldn't g-g-give your whereabouts."
Harry didn't say anything and walked away.
"Oh god," Hermione whispered, "He's going to be destroyed."
"I'll go," Ginny said quietly following.
"I can't believe he's gone." Neville said grimly, "But he died honorably. He didn't give any information and died to protect us."
"Draco can I talk to you?" Hermione asked after moment of silence, "Because that comment leaves quite a few questions."
Draco paled and nodded. Hermione walked away and he groaned, "She's going to kill me." He said before walking away.
"What did that mean, 'more than you know'?" Hermione asked when he reached her.
Draco swallowed hard not meeting her gaze, "I... I'm not going to lie here, Mione, I like you a lot. Like its past the point of liking by now. I don't expect you to like feel the same at all, but its not something I have control over and so I'm really really sorry if I've gone and made this all awkward and stuff and I'm really bad at talking about how I feel and stuff so I honestly have no clue if your understanding anything I'm saying, but what I leamt by that was I really love you and I-"
"Draco. Now is this time you shut up, and kiss me," Hermione said interrupting his ramble.
Draco stood there she'll shocked for a moment and Hermione laughed, "Bogs are so dumb," she said before wrapping her hand around his neck (not chokingly) and missed him.
Draco reacted instantly, having fantasized the moment where he'd get to kiss her multiple times a day, and didn't waste a second to slowly back her to the wall whilst gently holding her in his arms as if she was the most delicate thing he'd ever touched.
Right before he was about to pull away, Hermione mumbled four little words that made him forget the world.
"I love you, Draco."