The Strength of a Hundred Seal originated from Tsunade's grandmother, Uzumaki Mito. While it could be considered a technique of the Uzumaki clan, the truth was that no Uzumaki before Mito had ever practiced it.
The creator was Uzumaki Mito herself, and the reason for placing the seal on the forehead was simple—the tailed beast within her was sealed in her abdomen.
In fact, the Strength of a Hundred Seal had been developed specifically to counter the Nine-Tails, using vast reserves of chakra to suppress it.
The Nine-Tails had remained docile within Mito for so long, thoroughly subdued, not only due to her own formidable strength but also thanks to this seal.
Naturally, Tsunade didn't share these details with Hoshita Shūichi. Instead, she said, "Placing the Strength of a Hundred Seal in the abdomen is feasible, but how do you plan to address the issue we discussed earlier?"
Though she already had a solution, she wanted to test Shūichi's ingenuity.
Hoshita Shūichi smiled. "You must be familiar with the Four Symbols Seal, Tsunade-sama."
"I previously sought Minato-sensei's guidance on fuinjutsu, and he taught me this seal."
"My idea is to use two Four Symbols Seals alongside the Strength of a Hundred Seal, creating a cycle—one for input, one for output, without interference."
Tsunade fell into thought, mentally constructing the combination of the three seals.
After a moment, she nodded. "Technically, there's no issue with this design."
"And it's indeed better suited for your needs."
"However, this significantly increases the difficulty. Beyond mastering the Strength of a Hundred Seal, you'll also need to learn the Four Symbols Seal, which will take more time."
Hoshita Shūichi chuckled. "Though I do feel my chakra reserves are lacking right now, I'm not even seven yet. There's no rush!"
Tsunade didn't press further. "Very well."
"You can consult Minato about the Four Symbols Seal."
Cracking her knuckles, she added, "Since you're not learning the Strength of a Hundred Seal immediately, let's resume our sparring."
"Your chakra bursts still need work."
Hoshita Shūichi's eye twitched. "Wait, Tsunade-sama."
"Just because placing the seal in the abdomen is a good idea doesn't mean we should abandon the original approach."
Adults make choices. Kids take everything!
Nine-Tails Jinchūriki's Residence.
Jiraiya found Namikaze Minato here, studying fuinjutsu with Uzumaki Kushina.
Minato was overjoyed at his teacher's arrival. "Jiraiya-sensei, you're finally back!"
"Indeed!"
Recalling his time in the Land of Rain, Jiraiya smiled warmly. "It was quite a unique journey."
"So, Minato, have you completed that idea you mentioned before?"
Uzumaki Kushina, who had just brought tea, interjected, "Jiraiya-sensei, are you talking about the Rasengan?"
"The Rasengan?"
Jiraiya's excitement was palpable. "As expected of you, Minato! You've already finished it? Show me!"
Namikaze Minato grinned. "I wouldn't have completed it so quickly without Shūichi's help."
"Shūichi is one of my students now—a highly talented and exceptional shinobi!"
Jiraiya immediately recalled the polite, refined, and gentle boy he'd met earlier. "Ah, him! No wonder Tsunade took a liking to him. He must be something special."
"Jiraiya-sensei, you've already met Shūichi?"
Minato beamed. "Shūichi has indeed earned Tsunade-sama's favor. His talent in medical ninjutsu is outstanding. He's already a capable medic-nin in his own right."
Jiraiya chuckled. "Seems you're grooming him as your successor."
There was a difference between a student and a true disciple.
"Exactly!"
Minato admitted freely, then extended his right hand, palm up. "But for now, let's focus on the new technique."
Hum!
A swirling blue sphere—the Rasengan—formed instantly.
Jiraiya's eyes widened. "A flawless technique, perfectly suited to you!"
Uzumaki Kushina crossed her arms and cut in, "Jiraiya-sensei, this technique was developed for me! It suits me best!"
Not daring to provoke the fiery redhead, Jiraiya quickly agreed. "Of course! It's ideal for dealing with that Nine-Tails."
"The technique's power scales entirely with the user's chakra reserves."
Kushina sighed. "Right now, most of my chakra is tied up suppressing the Nine-Tails. Otherwise, I could use the Strength of a Hundred Seal to store chakra."
Minato reassured her, "Once you master the Adamantine Sealing Chains more thoroughly, you'll suppress the Nine-Tails more effectively."
"Besides, your chakra reserves haven't peaked yet, but the Nine-Tails won't grow stronger."
Kushina brightened. "True!"
"Hmph, I'll teach that Nine-Tails a lesson one day."
Watching them, Jiraiya couldn't help but think they were a perfect match.
One earnest, the other fiery.
Returning home from the hospital, Hoshita Shūichi began his formal training in the Strength of a Hundred Seal.
In simple terms, this seal involved creating a "reservoir" at the third eye acupoint to store chakra—like a water tank filled with chakra.
Unlike Tsunade, Shūichi needed two reservoirs: one large, one small.
The large one would store chakra for critical moments, while the small one would handle daily use.
Though cumbersome, this was his only option until he mastered the Four Symbols Seal and the Eight Trigrams Seal.
Unlike his earlier use of the "Seal-Memory Palace" technique, Shūichi's fuinjutsu had advanced enough that he no longer needed pre-drawn seals. Instead, he used hand signs to shape his chakra into咒 (fuin) characters, forming the seal.
Still, the process took a full minute.
"Strength of a Hundred Seal!"
With the final hand sign,tadpole-like spell (fuin characters) crawled across his body before converging on his forehead, forming a seal mark that soon faded.
Closing his eyes, Shūichi began channeling chakra into the two reservoirs.
October 6, Year 39 of Konoha's Founding: Hoshita Shūichi officially began his training in the Strength of a Hundred Seal!
To better develop new techniques and pursue the [Medical Expert] title, Shūichi reduced his out-of-village missions.
He spent most of his time at Konoha Hospital or training within the village, occasionally joining Namikaze Minato's team for missions.
Unnoticed, the temperature dropped—autumn was deepening.
One day, exhausted from training, Shūichi invited Tsunade to the hot springs. After being refused, he headed to Konoha's hot spring district alone to unwind.
"Huh?"
Shūichi noticed a figure on the rooftops.
"Jiraiya, that old pervert..."
He paused.
Peeping was immoral. It demanded severe criticism.
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