The 'water source' Hashirama mentioned refers to the amount of Chakra. So-called Senjutsu Chakra is formed only when Natural Energy and Chakra are maintained in a specific ratio. Once this stable ratio is lost, the Senjutsu Chakra disappears. Even more terrifying is when the Natural Energy exceeds the Chakra, causing the user to be consumed by the Chakra instead.
Relying on the spiritual power he had inexplicably obtained, Fūmori Masaki could obtain perfect Senjutsu Chakra without even needing to deliberately maintain it. Previously, he had no way to control the Natural Energy, which resulted in it continuing to pour in even after all the Senjutsu Chakra had condensed, leading to his critical illness. However, after learning to control the Natural Energy, he was unable to condense more Senjutsu Chakra due to a lack of Chakra, and thus could not unleash greater power.
The physique of the Fukimori Family members is not considered robust, and their Chakra is not very abundant. Although Fūmori Masaki is only eighteen now and his Chakra will increase with age, it would take at least until he is around thirty to potentially meet his requirements, and Fūmori Masaki cannot wait that long.
Fūmori Masaki hurriedly asked Hashirama if there was any way to rapidly increase Chakra. At first, Hashirama was somewhat puzzled by Fūmori Masaki's urgency for power, but upon reflection, he realized that Tobirama's other disciples were all brilliant and talented individuals. Apart from his aptitude for Sage Arts, Fūmori Masaki was not particularly outstanding among them; for a young man, this pressure must be immense.
After this period of guidance, Hashirama was very satisfied with Fūmori Masaki's serious attitude toward learning, and because the young man possessed an aptitude for Sage Arts, Hashirama also felt a sense of passing on a legacy to him. Thus, Hashirama pondered for a moment and decided to solve this problem for Fūmori Masaki; it was not as if he truly had no solution.
"Alright, since you are asking for it, I will give you an idea." Hashirama smiled at Fūmori Masaki and said: "If you want to increase Chakra, besides personal growth, you can only rely on external objects. Every clan has some corresponding heritage, and your family should be no exception."
Fūmori Masaki nodded. His family did indeed have some secret medicines to assist in a Ninja's training, but Fūmori Masaki had been taking them since he was a child, and they no longer had any effect on him. The secret medicines used for cultivation by other clans were likely the same, unless they were more potent and aggressive drugs, but the damage to the body would likely be significant as well, such as the Three-Colored Pills of the Akimichi Clan.
Could the Senju Clan's secret medicines be special? Fūmori Masaki looked at Hashirama with anticipation, but Hashirama said: "However, for a Ninja of your age, the effects of secret medicines are no longer very good, even those of our Senju Clan. But..."
Hashirama slightly curled the corners of his mouth and said: "Ninja secret medicines only have this much effect, but in this world, there are also some things that go beyond a Ninja's imagination."
"What kind of things?" Fūmori Masaki had originally been somewhat disappointed, but upon hearing the second half of the sentence, his heart suddenly stirred with excitement, and he asked hurriedly.
"Wait." Hashirama was not in a hurry to speak; he put his finger in his mouth and bit it until it bled, then quickly performed hand seals and slammed his hand onto the ground. In an instant, a large number of tadpole-like runes rapidly extended, forming a pattern similar to a magic circle, and then, with a 'poof,' a creature that was snow-white with hints of blue appeared before the two of them.
"This is..." Fūmori Masaki recognized the creature's true identity; wasn't this the Summoned Beast of Hashirama's granddaughter, Princess Tsunade, the Slug?
The Slug is a creature living in the land of Senjutsu heritage—Shikkotsu Forest. Unlike the other two lands of Senjutsu heritage, there is only one creature in Shikkotsu Forest, which is the progenitor of Sage Arts, the Slug Sage, and the Summoned Beasts of Shikkotsu Forest are actually all parts of the Slug Sage, that is, its clones.
Although Hashirama summoning the Slug surprised Fūmori Masaki somewhat, thinking about how Princess Tsunade would later also possess the Slug, and that Hashirama himself knew Sage Arts, it was not strange for him to have some connection to Shikkotsu Forest. The question was, what did the Slug that Hashirama summoned have to do with the things he had mentioned?
Fūmori Masaki immediately thought of the toad oil in Mount Myōboku. However, that stuff should only make it easier for people to absorb Natural Energy and has no effect on increasing Chakra. He was not very familiar with the other two places; the only thing he knew was that Jugo's Sage Body originated from Ryūchi Cave, while Shikkotsu Forest was a complete mystery.
In the original work of the other world that Fūmori Masaki had read, at least the White Snake Sage of Ryūchi Cave had appeared, but the Slug Sage had never appeared in a single frame. Come to think of it, since the Slug is just a clone of the Slug Sage, there doesn't seem to be much to look forward to regarding the appearance of the Slug Sage.
Hashirama did not know what Fūmori Masaki was thinking. When he saw the Slug appear, he greeted it, and the Slug looked at Hashirama and said: "Long time no see, Lord Hashirama. I didn't expect that you would actually have a time when you needed me."
The Slug's voice was very pleasant; just listening to it gave one a feeling of spiritual purification. Hashirama laughed and said: "I also have times when I need to ask for your help."
"Lord Hashirama, is there anything you need help with?" The Slug was very curious. With Hashirama's abilities, he basically did not need the help of a Summoned Beast. If he needed help with recovery, Hashirama could do it himself; if he needed a massive Summoned Beast for battle, Hashirama's wood construct could fight against a full-body Susanoo. Since signing the contract, Hashirama had basically never asked the Slug for anything; the only time was when Hashirama went to ask the Slug Sage about Sage Arts.
"Actually, I hope to borrow that thing in Shikkotsu Forest." Hashirama looked at Fūmori Masaki and said: "This child needs it."
The Slug turned around to look at Fūmori Masaki, lowered its head slightly, and said: "Hello."
"Hello." Fūmori Masaki responded, sighing inwardly at how good-tempered the Slug was. Those in Mount Myōboku were either bad-tempered or self-deprecating, and there was no need to mention those in Ryūchi Cave, who were basically all a bunch of cruel and tyrannical creatures. Shikkotsu Forest was simply a breath of fresh air.
"Since it is Lord Hashirama's request, there is naturally no reason to refuse." The Slug said, "Then please, Lord Hashirama, have this child sign the contract, and then you can take this child to Shikkotsu Forest."
"Mm." Hashirama nodded. Then, a puff of smoke suddenly burst out in front of the Slug, and a huge scroll appeared. Hashirama hurriedly opened it; there were many names written on the scroll, and the last person's name was indeed Hashirama.
"Come, Masaki, just write your name with your blood, and then leave your five-finger print, so that I can take you to Shikkotsu Forest." Hashirama said.
Fūmori Masaki was somewhat surprised that he was going to sign a Summoned Beast contract so quickly, and it was for Shikkotsu Forest, a land of Senjutsu heritage. His mood was truly a bit subtle. However, he did not hesitate; he bit his finger, used his blood to write his name on the scroll, and then left his five-finger print.
"Good." Seeing this, Hashirama nodded with satisfaction. The Slug immediately put away the scroll, saying that it would wait for the two of them in Shikkotsu Forest, and that they should wait a moment.
After the Slug disappeared, Fūmori Masaki asked: "Lord Hashirama, why exactly are we going to Shikkotsu Forest?"
"Because only in Shikkotsu Forest is there the thing you need. Although it can be brought out from Shikkotsu Forest, the effect would be greatly discounted." Hashirama said, "You only need to know that our Senju Clan's secret medicines use this thing as an ingredient, and you should know what kind of effect it has."
Fūmori Masaki was startled upon hearing this. The effects of the Senju Clan's secret medicines must be excellent. In addition to their innate physique, the secret medicines also played a major role in the Senju Clan's strength. He was now looking forward to what the thing Hashirama mentioned actually was.
After a while, Fūmori Masaki suddenly felt his body lighten. Immediately afterward, a sense of weightlessness washed over him, as if he were falling downward, and everything around him was replaced by darkness. Before Fūmori Masaki could react, the solid sensation of touching the ground came from the soles of his feet, and he hurriedly raised his head to look around.