In this fanfic all Naruto's stupidity and clumsiness was a mask

In this fanfic all Naruto's stupidity and clumsiness was a mask. He took it off after the Valley of the End. He is good at ninjutsu, taijutsu and kenjutsu (duo swords and katana) and fuuinjutsu (he's a natural genius in sealing). He is a 15 year old ANBU captain at the moment.

Prologue:

Blood. Screaming. Sounds of the battle. The scent of death was in the air. It was the downfall of Konoha. There was no way to win this battle, when Akatsuki and Oto joined their forces. Naruto couldn't believe his eyes: two enemy organizations worked together. He couldn't understand why this was happening. How?..His world was crushing down.

One by one his friends were dieing and there was nothing he could do to stop this. He was fighting with all he had, killing as many enemies as possible, but still there were too many of them. Feeling despair he used his father's famous Thundergod technique. Clearing the area he moved further trying to find where his friends were fighting, and after succeeding he really wished he didn't. Most of his friends were laying dead, their blood painting the ground crimson. Tsunade and Jiraya were fighting against numerous sound-nins. Hinata and Kiba were paired against venus flytrap looking Akatsuki member. Neji and Tenten fighting Kisame. Shino was using his bugs against Konan. But others…He wasn't sure if all of his friends were laying here, but after seeing one of the corpses pink hair, seeing Iruka's empty eyes and blood-covered silver hair…he didn't want to look anymore, he didn't care. He couldn't let his despair and pain to overwhelm him. So, instead he let his fury, hatred and desire for vengeance to overrule his senses, without letting them to cloud his mind and common sense. He became deadly and was ready to make his enemies pay for their crime.

Silence. The sound of wind dancing in the tree branches. Naruto stood in the middle of the battlefield, corpses of his friends and enemies around him. They were dead. All dead. He killed his enemies by using Hirashin no jutsu together with Kyuubis chakra. Akatsuki, sound-nins, Orochimaru…all gone…But it was too late already. His friends, his precious people, his family-were dead. His home ruined. He was standing alone on the enormous graveyard. His clothes were burned and tattered. His whole body was covered with blood: blood of his enemies, blood of his friends, his own. Blood was running from the numerous wounds on his body. His hair was falling freely on his forehead, somewhere during the battle he lost his hitae-ate. Standing on the wobbly legs he looked as if he will fall and join other corpses any minute…He didn't care. Naruto's ones vibrant, hypnotizing eyes were now dull and lifeless. Hollow. Eyes of the living dead. Inside of his mind Kyuubi was starting to get extremely worried about her kits sanity. Her kit never was so broken before, he never lost his will to live like he did now. She needed to do something and quick. Without hesitation she pulled him inside for a chat, deciding to take some action before it is too late.