Bang...
A teeth-grating sound rang out.
In the slowed flow of time, Naruto's fist, as large as a casserole, smashed viciously into 'Naruto Uzumaki's' cheek. The muscles in 'Naruto Uzumaki's' face rippled like waves, his mouth falling open as saliva sprayed out uncontrollably.
"Argh..."
'Naruto Uzumaki' cried out in pain. His gums throbbed terribly, and even his teeth felt loose.
Amid the pain in his gums, he was also deeply shocked. How had another him appeared? And this one was younger, more handsome, and, more frighteningly, even more hot-tempered.
Without a word of disagreement, he threw a punch, and with tremendous force at that, showing no mercy whatsoever.
While 'Naruto Uzumaki' was still bewildered, Naruto closed in and threw another punch at his other cheek. The last had been a right hook; this one was a left hook.
That way, it would be more even. One had to treat both sides fairly and not neglect the other half of the face.
As his fist struck another version of his own cheek, Naruto felt an oddly exhilarating sensation rise within him. So beating himself up felt this wonderful.
"Again? Are you insane?!" 'Naruto Uzumaki' burned with anger. He grabbed Naruto's incoming fist with one hand, ignoring the violent shock to the web between his thumb and forefinger, and activated Flying Thunder God without hesitation, taking Naruto away from the Hokage Building.
If 'Naruto Uzumaki' kept fighting in the Hokage Building, he would lose control, merge with Kurama, tear down the Hokage Building, and hammer this unknown version of himself to death.
The next second, the two of them appeared on the Back Mountain.
The Back Mountain was covered in trees. Fighting here would not cause much damage.
"Hmph, this is perfect. We won't damage public property here. Take this." Naruto saw