"Rrrrrrggggg....."
It was all Shusuke would hear in reply to his telepathic message; a low, drawn-out growl, much lower than the Inuzuka should have been capable of. As he looked between his two opponents, something condensed in the air.
Chakra. Keiyaku was enrobed by it, a thin, semi-transparent, black cloak surrounding him, exuding a strange kind of aura which permeated the air. Shusuke might have recognised something similar to this when Dove, standing at the village gates, had been possessed by some kind of spirit. While that spirit's aura, however, exuded tranquility and serenity, this one broadcast only anxiety and anguish, melancholy and paranoia. It hung in the air like a thick, choking miasma.
Time to dance....
Both boys' attempts to talk Keiyaku down fell on deaf ears, the Inuzuka not even acknowledging their speech, more so just watching them for signs of movement. Shusuke moved first. About a hundred spears had risen into the air, pointing at Keiyaku, the Yamanaka trying to use this as leverage to get him to calm down. Meanwhile, Kiri busied himself with gathering together dead forest fauna into humanoid shapes. With a great snarl, the entity raised Keiyaku's arm, and pointed a claw at Shusuke. There was a ripple through the air, and it was not immediately obvious to tell if anything had happened, but then the sound of clanking metal made it clear. The spears were revolving, jerking and rotating, ever so slowly beginning to aim away from Keiyaku and directly at Shusuke instead, as though the
gravitational force Shsuke's body produced had been increased by many orders of magnitude. Of course, it wouldn't be impossible to turn them back the right way, but there was no considerable force acting upon the spears. Kiri was the next threat. Shambling bodies composed of reanimated insects were charging ever closer, threatening to grapple the Inuzuka. Without even needing to form a hand sign, merely a flick of his wrist, each individual bug-zombie had its
center of gravity changed. The one charging down Keiyaku was flung sideways into a tree as though the vertical surface was now the floor; another was flipped upside-down; another was flipped sideways in midair. Of course, they could still charge Keiyaku down, but they would have to learn to compensate for the strange shifts in their centers of gravity. The Inuzuka seemed just on the point of charging down Kiri when...
"W-Wha..."
Keiyaku was twitching slightly, as though a mild electric current was messing with his nerve impulses. He looked at Shusuke, eyes trained on him. Though the Inuzuka's eyes still glowed a sickly yellow, they seemed to soften, and at once it was obvious Keiyaku was looking back out of them. But something was wrong.
The Genjutsu had worked, seemingly bringing Keiyaku back to himself, as though shaking him from a trance, but deep beneath the surface, a different game was playing out. Two souls were wrestling for control of a body, and Keiyaku was exerting every particle of his willpower to take back control, both of them at something of a stalemate. But this Genjutsu, this electrical current, had jolted Keiyaku's concentration, handing the opportunistic parasite dwelling within the Inuzuka a brief window to gain the upper-hand.
"Please...." stammered Keiyaku, his voice panicky but hoarse, and slightly feeble,
"pl-please hel-help me!!"
It must have been slightly disarming; the Inuzuka was usually brave and didn't lose his nerve for anything, but now his eyes conveyed nothing less than sheer terror. He looked at both Kiri and Shusuke in turn.
"I d-don't un-understand wh-what's happe-rrgghhh..."
Each time he tried to finish a sentence, it trailed off into a deep, rumbling growl, like some strange verbal tic that he couldn't suppress. It felt to Keiyaku as though something was forcing its way up his throat, threatening to burst out of his face. He was beginning to groan in discomfort, clutching his face, and the reason why was quickly obvious; something was moving underneath his skin, as though his bones were shifting for comfort. As he dropped to his knees, the groaning turned turned into a whimper, and for a time, the forest clearing was otherwise silent. And then...
It was as though Keiyaku had been suddenly lit on fire. The seal had loosened completely. His high-pitched shriek was one of pure, undiluted agony, and again, the reason for it was immediately obvious. The bones around his nose and mouth were pushing outwards, stretching his skin which was becoming slightly more coarse and leathery to compensate, his ears also stretching until they became sharp and pointy. At the same time, blood began to drip from his mouth; each one of his teeth, not merely his fangs, were becoming sharp, and engorging to an unnatural size, shredding through his gums until his mouth was filled with what were essentially short, jagged daggers. He was tilting his head this way and that as if trying to ease the pressure caused by his bones breaking and reshaping, pushing outwards to form a long, wolfish snout. At this point, his panicked shrieks had been extinguished, replaced by a rowdy, rumbling growl, drool seeping from his teeth.
This thing was only recognisable as Keiyaku by the slimmest margin. It was a mere glimpse of the thing inhabiting the Inuzuka's body; anyone with experience of Jinchūriki would recognise this as a partial transformation.
There were three solitary seconds of silence.
The creature tossed back Keiyaku's transformed head and let out an unearthly roar, like that of a tiger and a wolf's howl had joined together in some kind of unholy union.
And then, it happened....
On the coattails of the roar, it
was as if every particle of air had exploded like a bomb, rending it apart. With neither concentration nor hand sign to provide warning, a giant inundation of sheer, insurmountable gravitational force ripped out in all directions, sending everyone and everything flying through the air, with the transformed Inuzuka at its epicenter, still crouched on his knees. Even after recovering the participants of the battle would feel as though gravity had shifted, making it harder to walk Making up its mind in a second, it bounded after Shusuke, seemingly unaffected by the non-standard gravity, hoping to use the time created by its jutsu to tear into his throat, desperately swiping like a rabid animal.
After all, if Kiri was going to count himself among the ranks of the ANBU, teamwork was paramount.
[Sorry for the novel! I just found myself getting inspired, setting up Kiri and Shu's next big challenge]
The day had gone and evening was approaching it's close as the moon grew larger in the near night sky. The winds were chilly and the common caws and songs of the nighttime fauna were simply silent. Shusuke, or rather Reaper, was standing on a pole that housed powerlines. His dark cloak fluttering in the strong winds that took the evening, causing his form to wisp and whip. His cracked and broken mask laid resting in his hand as he waited. His gaze was unwavering. He had an assignment that he was glad to complete. He waited near one of his pupil's homes, keeping a sharp eye out for when the boy would begin to make his way home. It shouldn't be long now. 
