It was worth noting that Senju Mori was born with Water and Earth chakra natures.
As for the additional Wind-nature transformation, he had only mastered it slowly through long training and battles after advancing to jōnin.
For shinobi, being born with two natures was rare; for the Senju, Water and Earth carried a special meaning.
This discovery once made several Senju elders quite excited.
Even though Senju Hashirama himself was gentle by nature, the God of Shinobi's existence carried deep significance for the entire clan.
However—
Though Senju blood flowed in his veins, and though he was born with Water and Earth, Mori still could not learn the First Hokage's Wood Release that was said to "pacify the warring world."
The elders were disappointed, but Mori did not mind.
He knew that even if he could wield Water and Earth simultaneously and awaken Wood Release, its power would be no more than what Yamato would show in the future.
Without the Six Paths Yang power, Hashirama's own "Sage Body," and Sage Arts, it was impossible to reproduce that world-shaking might.
Rather than sink time into a jutsu whose symbolism outweighed its utility, it was better to learn techniques with real practical value.
With refined kenjutsu and taijutsu, plus mastery and skilled use of Water, Earth, and Wind transformations, Mori's strength now was not to be underestimated.
…
"Earth Release: Great Moving Earth River!"
In concert with the previous large-scale Water Release, Mori turned vast stretches of firm ground into patches of muck. Lush grassland became man-eating swamp in an instant.
Even a half–tailed-beast monster like Kinkaku had to obey physics so long as he could not fly.
Yet he was barely hindered. Like a true beast, he dropped to all fours, hands and feet sheathed in clawed tailed-beast chakra, and charged at Mori with all four limbs.
Clearly, the ambush had enraged him.
Mori's face did not change. He dropped to one knee and pressed his left palm to the ground.
At his touch, the earth around Kinkaku seemed to come alive.
The terrain flickered randomly between swamp and packed soil and stone. Even running on all fours, the uneven, nauseating footing nearly threw Kinkaku off balance.
At the same time, Mori formed one-handed signs with his free right hand. A forest of hard, razor-sharp earthen spears burst from the ground around Kinkaku, stabbing for his jaw, abdomen, even his inner thighs—
Too vile to meet head-on, the beastlike Kinkaku sprang off powerful hind legs to a nearby giant tree, kicked off the trunk, and pounced from the air.
Mori yanked back his left hand and rose, both hands flying through signs as his cheeks swelled.
"Wind Release: Sand Blast!"
As if the swamp's moisture had been sucked out in an instant, the ground cracked dry. Wind roared from Mori's mouth, hurling up a storm of dust that blurred everything in sight.
Such a blindfold would not stop Kinkaku's ferocity. In the next heartbeat he ripped through the dust, a claw driving through Mori's heart.
No blood spilled.
The "Mori" shape collapsed into viscous mud, then hardened in less than a second, binding Kinkaku's half–tailed-beast body for a moment.
In that heartbeat, Tobirama appeared behind him.
A super-high-velocity water blade sheathing the Second Hokage's right hand slid in with surgical smoothness, his arm's motion carving a widening lattice of cuts.
Stung to frenzy, bubbles foamed across Kinkaku's cloak, the chakra's red deepening to crimson.
Three more tails tore out of him in succession.
The suffocating tailed-beast chakra swallowed his features. In his eyes and gaping jaws only white chakra light remained, while a white exoskeleton began to form across his body.
A monster.
Kinkaku had become a monster. He needed no techniques; raw, uncontrollable chakra spilled out in waves.
Tobirama vanished without hesitation. Empowered and swollen with chakra, Kinkaku shattered Mori's Earth Release bind in an instant and raked a long furrow through the forest with a single claw.
To Mori's surprise, Kinkaku still retained some awareness. Those hollow white fox eyes snapped toward him.
He had sensed Mori's hiding place.
Boom!
The ground split with a roar. Kinkaku vanished and reappeared. Mori had no time to dodge; he barely hardened his skin with Earth Release before a single swipe hurled him away.
If not for the gouged marks left in the earth, Mori might have thought Kinkaku had learned Flying Thunder God mid-fight.
Thanks to earthen hardening, Mori survived being hammered into a rock wall, but the moment he opened his mouth, nausea surged.
He recognized the feel of compressed organs. Probing the impact site, he guessed at least two ribs had snapped.
An ordinary shinobi without hardening would have been pulped into a mist of blood.
Whoosh—
A massive chakra tail shrieked through the air again. Ready this time, Mori merged into the ground, slipping the strike and tunneling to Tobirama's side.
Tobirama's face grew paler, but his expression did not change; his voice stayed steady and calm.
"Don't worry. He isn't a true jinchūriki. His chakra and body's tolerance are limited. He can't hold this state for long."
"He's injuring himself, and what little consciousness he has left is fading fast."
"Once he becomes a brainless beast and then drops out of transformation, he may lose most of his combat ability outright."
"Then we—"
Mori's expression turned odd, a glint of eagerness flickering across his face.