From that point on, Konoha had a distinct advantage in the battle against Kumo; wherever Killer B showed up, they sent Kannin to help deal with him. This had the unfortunate side effect of sending Kannin all over the Konoha frontline, but adding a new piece to the board gave Orochimaru a lot of room to maneuver around Kumo, and, for the first time, Kumo was truly on the back foot.
This led Kumo to seek an alliance with Kirigakure to even the odds, which did level the playing field a bit, but the Hidden Mist's military power was not as strong as Kumo or Konoha due to so many of their own dying from the blood mist, so there was still a slight bias in favor of Konoha.
Similarly, the war against Iwa was going much better for Konoha after the destruction of Kannabi Bridge. After the bridge was destroyed, much of the Iwagakure army was left without critical supplies, and either defected, or retreated on its own. This afforded Team Minato a return home, but Minato himself was often called back to the front in case of emergencies.
Onoki had attempted one last big push into Konoha territory with 1000 of Iwa's best, but it was not only repelled, but by one man: Konoha's Yellow Flash. But it was during this time that another tragedy struck the Minato. While he was fending off the Iwa surge, shinobi had kidnapped Nohara Rin and forcefully made her the Three-Tails's jinchuriki.
-
Somewhere in the east of the Land of Fire, not far from Uzushiogakure, Kakashi had tracked the Kiri-nin who took Rin. Peering through the brush, he saw an entire outfit of Kirigakure shinobi leading a restrained Rin towards Konoha. He couldn't hear what they were saying, but Rin was looking worse for wear.
He waited for them to walk past before springing on them, taking out a few of them with kunai before separating Rin from them.
"Shit!" one of the Kiri-nin shouted, "Kill this kid!"
What Kakashi didn't know was that this was all according to their plan. With the seal they put on Rin, the Three-Tails would emerge as soon as they set foot in Konoha; they were only playing around in order for Kakashi to bring her back himself.
One of the Kiri-nin placed a genjutsu on him that blurred his vision after he engaged his improved chidori. As he was lunging at the enemy in front of him, Kakashi watched through his now hazy sight, as if in a dream--no, a nightmare--the silhouette of Nohara Rin lurching in front of his hand.
Kakashi had always divorced himself to the gore and bloodshed of battle, especially since he became renown as The Copy Ninja and his time on the front increased, but this time, he felt everything. He felt it as his hand slid through Rin's skin, then cracked her ribs, squelching the viscera beneath before piercing her heart and left lung, and emerging through her back. The blood poured.
The intense emotions ended the genjutsu themselves, clearing Kakashi's vision long enough for him to see the bloody smile of the one he swore to Obito he'd protect. An intense pain burst from his left eye, as his consciousness to start fading, but not before hearing a distant voice scream
"NOOOOOOOOOOOOOOOOO!!!"
-
Minato was busy defending against the 1000 man invasion on the Iwa front, and hadn't heard about what happened until he returned to Konoha to see Kakashi staring at a grave in the funerary district. Without a word, he came closer to look at the grave, and saw the name on it.
Grief wasn't something that entered Minato's mind that often. While he was goofy and childish at times, he was still a ninja, and that meant dedication to his mission and to victory. The only other times he had felt immense grief was when his own parents died in the 2nd war, and those many months ago when Obito died. Now, he once again felt a shaking in his legs creep up and choke him.
'Why is it that even with Flying Raijin I'm never where I need to be...' He thought.
He didn't let any tears fall from his eyes as he walked up to Kakashi and asked him what happened. Hearing the tale, Minato's eyes fell. The deaths of Obito and now Rin were already weighing on him like boulders, but as he heard that Kakashi himself killed her, he couldn't even begin to understand how he was feeling.
"Kakashi..." He said, trying to find the right words, "this is my fault, okay? I've messed up twice, and each time you've suffered. You can't blame yourself for this."
"Sensei," Kakashi said with sorrowful eyes, "I don't have anyone left."
Those words broke Minato's heart. He had known Sakumo for a short time before he passed, and of course he knew Rin and Obito--all of Kakashi's closest friends and family were gone.
"Kakashi," he said, putting his hand on Kakashi's shoulder, "that isn't true. You still have me, right? And what about your jonin friends, huh? What about that Gai kid? All's not lost, okay? Promise me you'll keep going no matter what."
Kakashi stared at the ground for a moment, tears streaming down his face, before slowly nodding his head.
"One day, and I believe that day is soon, this war will be over. That's when we can start to fix what was broken, create new connections, and honor those who fell."
-
When Minato returned to his home, he saw Kushina sitting on the couch by herself, looking at a picture with reddened eyes. As he entered, she looked up at her husband, and saw his eyes had darkened.
"I imagine you heard." She said, with none of her usual joy
"Yeah..." Minato began to speak, and after a long pause said, "Honey, what do I do? I'm a failure as a sensei."
"Not yet," she said, "you still have Kakashi, yeah?"
With a thousand yard stare, Minato muttered softly, "Yeah, there's still Kakashi. All's not lost. I told him that, but I don't know if I even believe it..."