Karin felt physically and mentally heavy when Sasuke stabbed through her to kill Danzo. Her body was weak. Her mind was groggy. It was difficult to move or form thoughts, so she stopped trying. She lay on the ground, bleeding to death.
Karin glanced up at Sasuke, focusing her eyes so she could see his face one last time before he finished her off. She would have let him, too, but that was when Naruto, Sakura, and Kakashi arrived and intervened. They healed her and decided to take her back to Konoha with them. As she started to recover, a new weight settled on her. She felt emotionally heavy. Sasuke, the man she loved, had just tried to kill her.
What was she to him? Nothing more than a walking first aid kit, perhaps. He clearly didn't love her back, and she was overwhelmed by how much that upset her. Her heart was completely weighed down. It was a good thing she was being carried, because she didn't have the will to move on her own.
Karin had decided that she was done with him. She didn't need him. Of course, she was lying to herself, and she knew it. She still loved him, wanted him, needed him. She didn't even know why. Why she still bothered to care, when he obviously didn't.
When Karin had been brought to Konoha, she was interrogated, though she didn't give up any information. She wanted to protect him. More importantly, she wanted to escape so she could find him again. She didn't know if he would want her back, but it was a risk she was willing to take.
Once the interrogation was over, she was put in a jail cell. A sort of heavy calmness settled over her as she prepared to break out of jail and return to him. First, she would need the guards to pay less attention to her. To do that, she would make them think she was crazy.
Karin began cooing about Sasuke. Then she began screaming about him. She cooed again. She screamed again. Repeat. Repeat. Repeat. Eventually, her guards deemed her completely unstable and incapable of breaking out, and they stopped paying attention to her. They'd even grown bored and started playing cards on the floor.
At that point, while continuing her ramblings about Sasuke, Karin removed her glasses and took out the small blade that was hidden in the right arm of them. Putting them back on, she crept toward the door as quietly as she could and silently began working the lock open with the blade. After a few seconds, she heard a click and shoved the door open, making a run for it before the guards had time to process what was going on.
Pausing in the shadows of an alley and breathing heavily after being chased across rooftops by the authorities, Karin was sure she'd lost them, at least for the moment. She began tracing Sasuke's chakra, and it wasn't long before she found it. It was surprisingly close. He was near the village, which made reaching him easier.
As Karin followed his chakra, the thought of seeing him again made her feelings fluctuate. Her heart would soar with happiness and excitement, then it would sink with sadness and anger. However, she was determined to be with him again, not just out of love, but out of loyalty. There was something else, too. She wanted to prove that she wasn't useless.
Karin was getting close to where she sensed Sasuke to be, but stopped in her tracks. What would he say to her? What if he tried to kill her again...and succeeded? Should she even bother? She was about to turn back, but stopped herself. Shaking off the negative thoughts from a few seconds before, she told herself she wouldn't quit now, not when she was so close. She kept going, and could soon see them in the distance.
Sasuke, Juugo, and Suigetsu, as well as the reincarnated Orochimaru and first four Hokages, were getting ready to leave for the battlefield and fight in the Fourth Shinobi World War.
She sped up until she reached them, standing before them. The first person she saw was none other than Sasuke himself, and seeing him made all her emotions bubble to the surface and burst forth. She screamed at him about how she would never forgive him for what he'd done, about what a horrible person he was. He simply said that he was sorry, but to Karin, it meant a lot more than that.
Sasuke had never, ever apologized to anyone. He was emotionally distant, so something like this, which would seem small to anyone else, was huge for him. Karin really appreciated that, and that's when she realized that it wasn't the first time he'd made an effort.
She remembered the time he told her he needed her. The time he told her she'd saved him. The times he told Suigetsu to leave her alone. The time he'd used his Susano'o to catch her when she was falling. The time he'd used his Mangekyo to save her from Amaterasu's deadly black flames.
She realized that maybe she truly did mean something to him. Yes, he tried to kill her, but it made sense when she remembered that he became darker and colder during his fight with Danzo because he teased Sasuke about Itachi, making him determined to kill Danzo at all costs.
Unable to contain her excitement at this revelation, she hugged him and forgave him. The group then left for the battlefield.
The last time Karin felt heavy was the worst, the heaviest. It was during the war, when Madara fatally injured Sasuke and left him to die. When Karin looked for his chakra signal, she found a weak one, quickly growing weaker.
Realizing what that meant, she sank to her knees in shock and cried, holding her head in her hands. She said his name several times, afraid that he really would die. Then, she stopped sensing his chakra altogether, and she rose to her feet, convinced that she could still save him.
Rushing into the battlefield, the Uzumaki Chakra Chains shot out of her back, destroying part of a giant wooden statue that was attacking the Allied Shinobi Forces. She was impaled by it in the process and bit herself to recover, determined to get to Sasuke before it was too late.
Once Karin, Juugo, Suigetsu, and Orochimaru reached Sasuke, they found that he had been healed by Kabuto. She was relieved, to say the least. It felt as if the weight of the world had been lifted from her shoulders, and she'd proven that she wasn't useless.
The very moment the war was won by the Allied Shinobi Forces, Sasuke turned to Karin, grabbed her shoulders and pulled her into a hug, catching her by surprise. She crumpled into him, and he whispered in her ear, "I'm sorry for everything I've done, but thank you for everything you've done."
"Shut up and kiss me," she said, wrapping her arms around his neck as they kissed deeply and passionately. The war had changed him for the better, and for once, she felt weightless.