Kakashi had spotted an Iwa-nin hiding in the mushroom-ridden forest ahead, and without hesitating activated Chidori, or his still half-baked version of Chidori. The chattering of a thousand birds filled the air, crackling and squeaking as lightning coalesced in his hand. Rin and Obito were both surprised and afraid of the technique, since it didn't look like Kakashi had full control over it.
Minato was also not enthusiastic about the technique--it simply wasn't complete. And while there was always a first time for everything, you never go in with a jutsu you don't fully understand or can't fully control. He urged Kakashi to have some more prudence, but Kakashi simply said: "It's a rule that the student follows the commander's instruction, isn't it?" Which elicited a head shake from Minato.
He sensed at least 20 chakra signatures, which either was a large force, or a Kage Bunshin. Kakashi was being arrogant and hasty. Thankfully, Minato was able to protect Kakashi from the incoming kunai by intercepting them with his own. However, a shadow clone came out to Rin and Obito to attack them, and he had to fend him off as well. Ultimately, he had to save Kakashi as well, and even then he got injured, and take out the real Iwa-nin hiding in the trees.
Minato knew Kakashi was a formidable shinobi, but he couldn't lead because he couldn't consider his teammates in his plans. While disappointed, he reminded them that teamwork was the most important thing on a mission, especially since he had to leave to the front after this. After his admonishment, he left.
Appearing on the front, Minato was astonished. There were only four of them. Jiraiya said there'd be at least 100 times that. Furrowing his brows, he quickly asked for a sitrep.
"There's only four of us, and at least 50 enemies."
'Hmm, not the best odds, but well within my capabilities' Minato thought.
He quickly handed out his special kunai to the 4 of them and ordered them to toss them across the battlefield, all the while praying that Kakashi and the others were doing alright.
Clearing his mind of everything but the battle, Minato took a deep breath, and exhaled. He jumped to the first kunai, and killed the nearest man to it, then jumped to the next, then the next, then the next... It was a pattern Minato had gotten used to during the war. In a flash, 20 of the enemy were dead. Another moment, 25.
The 4 Konoha-nin looked on in shock, and a little horror too, as the Yellow Flash lived up to his name. All they could discern was a yellow streak flying across the enemies, who promptly fell down, dead before they hit the ground.
Minato did make rather short work of the Iwa shinobi, and quickly returned to the Konoha nin.
"Alright, all that's left is to get you guys back to base, yeah?" He said
They nodded and packed their things. It took a minute for Minato to collect his kunai again (they weren't cheap, you know), but after that, Minato began escorting them back to base. Less than an hour after that, Minato's heart dropped as the formula he placed on the kunai he gifted to Kakashi activated. Without a word he teleported to his location.
What awaited him there was a scene which would draw out from him a feeling he realized he had never truly felt before. He saw Kakashi wielding his chidori collapsing and Rin behind him, cowering, as Iwa-nin were descending upon them both. As soon as Minato comprehended 2 instead of three, his eyes went cold, and a fire lit in his heart. Iwa-nin had driven Konoha's Yellow Flash to rage.
After killing the enemies, he turned back and saw Kakashi on the ground, passed out, a scar covering his left eye. It took a moment for him to calm down while he carried Kakashi's unconscious body.
While they ran, Rin told him what happened, at least what she knew: she was captured, and the genjutsu put a void in her memory, but she remembered their escape, how Obito pushed Kakashi from the falling rocks. It seemed like Obito finally awakened his Sharingan, which made Minato proud. She also told him that she implanted his eye into Kakashi's left eyesocket.
'So that ended up being his gift, huh?' He thought with a sad smile, 'It sounds just like Obito--he couldn't realize his life was enough.'
Minato did his best to contain himself as they went, and especially after Kakashi woke up. When he did, Minato saw a red eye where his usual black one was, with two tomoe floating around the pupil.
Minato held them together long enough to complete the mission, though--and with a taste of revenge coloring their eyes, Kannabi Bridge was destroyed.
Kakashi changed after that. He was, for lack of a better word, kinder--no longer obsessive over emotionlessness and self-sufficiency. He looked deeper at things, but never directly at them, still always distracted by the two great losses in his life, first the father, then the friend he didn't know he had. Minato despaired to think that losing Obito was what it took to make that change for him. He just hoped Kakashi could forgive himself one day.
Minato was given a brief leave after that, as is customary if one loses a team member, and is customary if one of the most powerful shinobi in the village demands it. Minato needed to see Kushina.
Knocking on the door, he waited for his beautiful wife to open the door. When it creaked open, and Minato saw her, it was almost enough to take his mind off losing Obito, almost. She tried to ask him how he was, but she could tell, deep down, that something had happened. He wordlessly hugged her, and she dragged him through the threshold to their table. There he told her what had happened.
Kushina's face sank as she heard him, with his head hung low, explained it. That little Uchiha boy that was going on about being an elite and Hokage one day was gone. She ran her hands through his hair, and realized that, for the first time since they had started dating, the cool and calm Namikaze Minato was crying.
"He was just a kid..."