However, with Karin present, the situation became much easier. Extracting around 3,000 units of life energy from her was sufficient to activate the gene medicine. Since this amount was well under 10% of her total life energy, it was akin to donating blood—causing only mild fatigue and no serious harm. Despite being only a genin, Karin's reserves were massive.
Truly worthy of the Uzumaki clan.
[This time, it doesn't even require 10% of the donor's life energy?]
Kimimaro recalled that when activating the Taketori clan's bloodline medicine, he had used a portion of Taketori Ginro's flesh and blood essence after death. That essence held roughly 10% of a person's total life energy.
Yamato's case had been similar—10% life energy was the benchmark for activation.
[Actually, every bloodline gene medicine requires a fixed amount of life energy to activate. The reason the previous two seemed to demand more than 10% of the host's life energy was simply because those hosts had less total life energy to begin with. For example, activating a Hashirama-based medicine might take 50,000 units. But with Hashirama's immense vitality, that 50,000 wouldn't even reach 10% of his total.]
That explanation made sense to Kimimaro. Yamato likely had over 100,000 units; Hashirama could easily have been close to a million. Life energy wasn't the same as chakra, but they scaled similarly for comparison.
Kimimaro carefully extracted 5,000 units from Karin, reaching just about 10% of her reserves, and stopped.
"How do you feel?" he asked.
"A little dizzy," Karin replied, brushing a strand of red hair behind her ear. "But I'm fine. It doesn't affect my movements." She tilted her head. "Is that all?"
"No. It still needs to be processed—it'll take around two days."
Now that his strength had increased, both his absorption limit and his conversion speed had improved. What had once taken three days now took only two.
As for the absorption limit…
"Fū, lend me your energy too."
This time, he extracted 15,000 units. As the Seven-Tails' jinchūriki, Fū had life energy far beyond that of most shinobi. Even this amount was well under 10% of her total.
But Kimimaro couldn't absorb any more right now—he had to process the current 20,000 first.
The original 20,000 units he had stored had mostly been used—7,000 for Yamato's medicine, another 5,000 for manufacturing supplementary test tubes. Now, with an added 20,000 in reserve, and an upcoming 3,000 + 6,000 usage for the Uzumaki medicine over two days (including a daily 200-unit time reduction cost), his reserves were finally recovering.
Kimimaro glanced over at Jūgo.
These two are my biggest life energy reservoirs. Karin can rest and recover now. In two days, I'll tap into Jūgo for a refill. Since we're being honest with each other, we might as well all contribute.
If the system allowed him to use his own life energy, Kimimaro wouldn't hesitate to donate it.
"Which bloodline are you planning to fuse into me?" Karin asked, a little excited. "Didn't you say you could graft bloodlines onto others too?"
"Whichever one you want," Kimimaro nodded. "Once I have it stabilized, I'll give you a choice. The same goes for Jūgo and Hanabi. But remember—I'll also need a sample of your bloodline to refine the compatibility."
"But… Big Brother," Hanabi said hesitantly. "Our Hyūga clan doesn't allow bloodline transfer. We're very strict about who can inherit the Byakugan."
Kimimaro crouched down to meet her gaze. "Hanabi, your bloodline is essential to me. My old condition—my clan's sickness—still lingers. I need the Byakugan to refine my body and correct the flaws. Don't worry—Uncle Hiashi won't blame you."
"Really?"
"Heh," Karin added slyly, "your dad's probably already hoping you'll marry Big Brother in the future. What are you so scared of?"
"Huh?!" Hanabi's face turned bright red. She glanced at Kimimaro, who didn't deny it—his expression unreadable. That made her blush even deeper.
After a long moment, she finally whispered, "I'll listen to Big Brother…"
Two days passed. The absorbed life energy had fully converted. Kimimaro immediately withdrew 3,000 units—specifically from Karin's share—and activated the medicine.
Then, he invested another 6,000 units to accelerate the process, and the Uzumaki bloodline gene medicine was finally complete.
He still had just over 20,000 life energy units stored in the system.
Fū was excited, her green eyes full of anticipation. She still had some doubts—was it truly possible to fuse someone else's bloodline into her body?
The Uzumaki clan didn't have a Kekkei Genkai, strictly speaking, but their physical constitution was nothing short of legendary.
Just by life energy alone—a normal genin's life energy hovered around 500 units. Karin had 50,000. That surpassed even many elite jōnin.
And it wasn't exaggerated—life energy accounted for not only chakra but also one's physical body, stamina, and inherent spiritual resilience. Chakra and constitution were two dominant factors in that total.
The Uzumaki physique truly was a monster-class trait. Think about it—most shinobi could only manage one or two Shadow Clones at a time. Naruto could create hundreds—thousands—without breaking a sweat.
That wasn't just the Nine-Tails at work. It was the Uzumaki bloodline.
Kimimaro inserted the needle. The gene serum entered Fū's body slowly, merging with her life stream.
Her eyes began to shift.
"Everyone, stand back."
Kimimaro immediately gave the order, and Karin, Jugo, and Hanabi quickly retreated to a safe distance.
Inside the clearing, Fū screamed in pain—her body wracked by the strain of forced gene recombination. Chakra erupted around her like a storm, coalescing into a Version 2 Tailed Beast Cloak. Several insect-like tails of pure chakra whipped violently through the air, destroying everything in their path.
"She's losing control…!" Kimimaro muttered. His eyes narrowed. Without hesitation, he formed a seal.
"Wood Release: Great Forest Technique!"
Thick wooden tendrils burst from Kimimaro's left arm, racing forward to entangle Fū. The chakra tails struck back violently, tearing apart several branches, but Kimimaro forced the jutsu to hold.
Then he raised his right hand.
"Kōan Ichinyo!"
A glowing kanji—座 ("seat")—appeared in his palm. This technique, a simplified version of the Hokage-style Suppression Jutsu, was inspired by the method Hashirama Senju once used to subdue the Nine-Tails. Though Kimimaro's power and Wood Release were far inferior to Hashirama's, the jutsu still carried a hint of mental suppression, enough to potentially reach Fū's consciousness.
But it wasn't enough.
The cloak intensified, and the Seven-Tails' chakra roared. Fū's body hunched over, her features distorted by the beast's influence. A ball of compressed chakra began forming at the mouth of the cloak.
"A Tailed Beast Ball?!" Kimimaro's breath caught.
This wasn't something he could tank—not even close. But he didn't retreat.
"Fū! Can you hear me?" he shouted. "Don't fight the Seven-Tails—talk to it. You're an Uzumaki. That bloodline was once known for powerful sealing techniques and unparalleled chakra control. You can do this!"
The Tailed Beast Ball stopped expanding—but didn't vanish.
"You've trained for this," Kimimaro said firmly, standing his ground. "Think about how you always smile when you're with us. You're not a monster, and neither is Chōmei. You two can coexist."
The wild chakra trembled. Fū let out a ragged cry. Her eyes—once bestial and red—flickered, then slowly returned to their usual vibrant orange.
Kimimaro didn't move, even as the swirling Tailed Beast Ball hovered, half-formed, just meters away.
"I trust you, Fū," he said softly. "You'd never hurt your friends."
Moments later, the chakra sphere began to shrink, then dissipated entirely into harmless motes of light. The Tailed Beast Cloak peeled back as well, retreating until only Fū remained, panting, on her knees.
"I'm… sorry," she gasped, tears forming at the edges of her eyes. "I really couldn't control it for a moment."
Kimimaro offered her a hand. "That's why we're here—for each other."