Sasuke, along with Team Taka and the four Hokage, arrived at the battlefield right in time, when Madara was about to use the Juubi once again. He ordered Karin, Suigetsu and Juugo to help the rest of the Shinobi forces, while he and the Hokages would head to Naruto and Madara.

"Sakura-san!" she yelled when she spotted the worn out medic.
"Karin-san?"
Sakura was surprised to see the red haired girl on the battlefield as she knew they would be keeping her under surveillance in Konoha. How did she escape Ibiki's men so easily?
"Karin-san, why are you here?"
"Sasuke is also here, we came to help!"
"Sasu..ke..?"
Sakura was shocked to hear his name so suddenly. He came to help.. But why..?
"Oi, Karin! We're also here!" a male voice sounded from behind Karin and stood right beside her.
"SHUT UP, SUIGETSU!" she yelled back at him and punched his face, but as usual, he dodged it and liquefied himself.
"Anyway, Sakura-san, are there any wounded that I can heal?"
"Huh?.." she came back to her senses and answered her.
"Yeah, over there!" she pointed at a group of shinobi who had been taken to safety in a nearby cave.
"Alright!"
She knew what to do now. In order to impress Sasuke, she had to do her best on the battlefield. Since she wasn't much of a combat fighter, she had to rely on her healing abilities. A lot of people needed her right now.
"Suigetsu, Juugo, you'll form a shield for the Medical Troops! Got it?"
"And just who are you to order us around?" Suigetsu frowned and crossed his arms, glaring at the redhead. She stepped back and nervously fixed her glasses.
"W-W-Well… Y-You wanna be of some help to Sasuke, don't you? Being guards is perfect!"
She let out a fake laugh and looked down.
"Sigh.. Ok." He agreed to become her shield and protect the injured. Juugo didn't even question it, he immediately transformed and stood in front of the wounded like a protective wall.
Karin hurried to Sakura's side and begun treatment. She couldn't extract any chakra from her body by herself so the patients had to bite her multiple times. It wasn't like when Sasuke did that. She enjoyed it pretty much when he dug his teeth into her skin. But that only happened three times. Now she had to be beaten multiple times in order to help the injured. It was a bit painful, but she had to bear with it.

Suigetsu and Juugo defended the medical ninja and repelled every attacks from the remaining Zetsus. Everyone else was doing their best at the front lines, against Madara and the Juubi.
Suigetsu didn't have his ninja sword anymore so he had to use his Clan's water jutsu to build up a robust defense. Karin always looked back to see how the two of them were doing. She had to admit that she was a bit worried about them. Maybe it wasn't like her to show how much she cared, but she actually was very relieved to see both of them when she escaped the interrogation prison.
"Please be careful boys" she mumbled to herself.

She could hear how much they both struggled, doing their best. Sakura had left to help at the front line and Karin was left by the wounded, together with two more medical ninja. She had almost run out of chakra. Juugo had also already reached his limit. He begun to transform back to normal. Suigetsu covered his back and attacked one of the Zetsu's who aimed at his friend.
"Juugo, you ok?" he asked concerned.
Gasping for air and being totally exhausted he replied "Yeah.." and tried to gather up all the strength he had left.
Suddenly, an unexpected kunai came from behind and scratched Juugo's left leg. He fell down on his knees and held the wound with both of his hands. Suigetsu turned around to see what had happened to him and rushed to repel the following attacks.
"Get up and go to Karin! She'll heal your wound and lend you some chakra!"
"But she's almost out of chakra herself.."
Suigetsu looked towards the direction of the Medical Troops and saw Karin treating an injured shinobi. She really did look worn out. Her face expression was neutral though.
He looked back at Juugo and sighed again.
"I wonder to what extend I'll go for the three of you, really." he smirked and turned his attention to the enemy.
"Suigetsu!" Juugo screamed as he saw his friend heading to battle alone.
"Don't worry , I'll be fine!"

Juugo hurried to Karin to tell her what Suigetsu intended to do. They couldn't leave him alone. He would definitely get killed.
"He did what?" Karin looked at Juugo in shock.
"We need to help him! He can't pull it of alone.. but my chakra is not enough.." Juugo had almost no strength left and collapsed right in front of her. Still conscious, he told Karin where Suigetsu went and assured her that he could leave him behind and go search for their teammate.

She run as fast as she could. It had also started raining. This day seemed endless to her.
"Suigetsu! Suigetsu where are you?" she screamed while running.
The rain drops were blurring her glasses and her wet hair fell on her face, but she didn't care. Her legs were moving on their own. She didn't even know where she was going.
"SUIGESTU! ANSWER ME DAMMIT!"
She screamed even louder and stopped for a moment to look around. She spotted the boy fighting with one of the Zetsus near a crater that was caused by an explosion, maybe by a paper bomb. The whole place was covered with these.
"Suigetsu!" she screamed one last time and tried to climb down to the bottom of the crater, but the ground was too muddy and she fell, dirtying her clothes and dropping her glasses.
"Karin, get back!" he yelled at the girl.
Suigetsu was exhausted from all the fighting he'd been dealing with. The Zetsu changed form and disappeared into the ground.
"Karin, quickly, get out of here!"
He suspected that the Zetsu would be heading for her… and he was right. While she tried to stand up, something pulled her back by grabbing her foot. She attempted to shake it off, but it just wouldn't let go of her.
Siugetsu used a sword he had picked up while battling another Zetsu and cut the creature's arm which held on her leg. With Water Style he formed a barrier around the girl and turned around the finish off the Zetsu.
"Suigetsu!" she punched against the barrier, but it was no use. He used water from his body to form it, that's why it was resistible enough to keep her safe inside.
The blade he had picked up wasn't as strong as the Ninja Swords of Kirigakure, but he had no other choice.

It looked like the Zetsus were increasing. But he wasn't strong enough to pull them all away. He had to stop his body's water-jutsu and materialize himself completely. The barrier around Karin broke and she was exposed to the Zetsus once again. Suigetsu told her to stay put and lower herself. He had once last strike left. He had to finish them all at once, or else she would be in danger.
Closing her eyes, she covered her ears with her palms and sat down, praying for his safety.
But when she opened them… he was down.

"S-Suigetsu..?" she slowly tried to stand up, following the sense of his chakra as she couldn't see a thing without her glasses. His chakra was very weak, almost invisible.
She reached the point where he was laying and kneeled down.
"Suigetsu?.. A-Are you.. ok?"
Her voice was trembling as she reached out for his hand. When she touched his cold body, she started welling up tears.
"H-Hey.. S-Suigetsu!"
"Ka… rin…" he weakly replied.
His body could not alter itself anymore. He had depleted his chakra. She gently took his hand and looked down desperately, while sobbing.
"O-Oi… don't tell me… you're… crying…"
His tone was a bit sarcastic and derisive. He never would have thought that she'd show him a face like that.
She suddenly gasped and looked at him while a single teardrop escaped her eye. She heaved up her sleeve and held her arm before his mouth.
"Here! You have to bite me! Quickly!" her words were clear now. She wanted to save him, although she herself wasn't in best condition either.
She never got along with him, ever since they first met. But still, she felt unease when she didn't know what was going on with him. All the time she spent with Team Hebi (and later Taka), she felt like those guys had become her new family. Juugo was like the mother, always carrying her when she was exhausted. Sasuke was her crush, of course. And Suigetsu… well, although they were fighting the whole time, he kind of seemed like a brother to her. She knows that he would help her at any time. Now it was her turn to repay him for all the good memories.
"Come on! Open up!" she tried to make him open his mouth, but he couldn't speak anymore. He barely even breathed..
"Suigetsu!"
Her voice became teary again and her body was shaking in fear.
"No, no, no, no! Wake up you sloppy bastard!"
She put her hand on the back of his head and slowly lifted it, placing his upper body on her lap. A tear fell on his cheek, sliding down to his lips.
"I won't.. let you die.." she mumbled in a trembling tone.
"I WON'T LET YOU DIE, OK?"
Her emotions burst out all at once and her crying became harder.

She bit her under lip until it begun bleeding. There was no other way. She had to give him chakra somehow.
"Hold on, Suigetsu!"
She lowered her head, becoming face to face with him. Her eyes scanned his damaged skin and his dirty white hair. A drop of blood fell on him. She took a deep breath and closed her eyes, pulling her lips against his and biting them. Their blood was connected and she could now transfer her chakra… but after a minute she realized that it was not enough.
Desperately, she tried to ingest her chakra by biting him several times, but his body wouldn't respond.
"SUIGETSU~!" she screamed and cried over him.
"SOMEONE PLEASE HELP ME!"
Not a single soul was around to hear her cries and mourns. It was too late for any help…

Putting her hand on his chest, she felt how motionless he was. His breathing had stopped.
She leaned forward and placed her forehead on his. Her tears rained on him and her red hair covered his peacefully slumbering face..
"You… idiot…"

And so the rain had stopped…