Takara found himself aboard a not-so-luxurious ship heading to the docks of the Land of Water, from where he would make his way to the capital. In his cabin, filled with seals around him to block any possible nosy sailors, he was letting Katsuyu, perched on his bare shoulder, perform a check of his talent for Senjutsu.
It turns out there was a way to measure talent or compatibility for learning the sage mode. In Katsuyu's words, the snakes were too lazy to bother since they wouldn't gain anything, and the toads say they believe everyone should have a chance.
As long as they're their allies.
In fact, she even commented that the talent of Tsunade's former comrade, Jiraiya, was terrible and he shouldn't be able to practice the toad sage mode. Apparently, the solution they found was to secretly add a diluted version of toad oil to the insect meals Jiraiya made during his stay at Mount Myoboku.
This resulted in him being able to use a pseudo sage mode with the help of the two elder toads, but at the same time, it prevented him from going further and perfecting himself, becoming dependent on the toads.
Katsuyu didn't beat around the bush and told Takara that she was sure the toads did it on purpose; they always liked to be in control.
"And how is my situation?"
Katsuyu had been examining his constitution for an hour without haste, and Takara really didn't want to hear that he was worse than Jiraiya; it would be humiliating.
"Complicated," the slug replied with her soft voice, "but positively complicated."
Takara didn't reply but stared at her, waiting for her to continue explaining his condition.
"Your chakra control is exquisite, your lineage conflict seems to be stable, and due to the effects on your body during your growth from the Ryumyaku fragment your mother gave you, you should be able to practice Senjutsu much more safely than others," explained Katsuyu as she moved her eyes. "If I had to rate your talent, you would be around an eight out of ten, and slightly more. But adding the Ryumyaku, you would barely reach nine, which is already quite high. Think that ten represents the capacity Hashirama Senju had in his prime."
Takara was fine with that result; more than seven would have been more than enough for him.
"What would your assessment of Jiraiya's talent be?" he asked out of curiosity, wanting to know how bad he was.
"A solid two, reaching three with the help of the oil and the elder toads," ruthless words for such a soft voice, "But let's not talk about the pervert. If you really want to master Senjutsu, we should start practicing."
"How should I do it?"
He knew how the two methods of the other sage lands worked, but nothing was known about Katsuyu's.
"I have different ways for different levels of talent," replied the slug with a subtle tone of pride as she lifted her head. "With yours, the most appropriate would be for you to eat me first."
"...Excuse me?" Takara wasn't sure if he heard wrong.
That left him perplexed, no, completely stunned.
"The toads use toad oil to create an external stimulus on the skin of their practitioners, while the snakes use their fangs to directly inject natural energy inside. In both cases, they use something 'foreign' to what the human body is accustomed to, and that makes it easier for things to go wrong and for there to be rejection," Katsuyu explained patiently to give context to her idea and not to seem like an absolute lunatic with a fetish for being devoured.
"I can divide myself into much smaller versions, so if you swallow one of them, your body will digest my clone. In doing so, I will make it become part of your body and adapt better to the sage mode. This way, we can later use my slime to help you practice, and since your body will process it as 'yours,' everything will be smoother and less dangerous."
"So..." Takara processed the information and realized, "You use a combination of both. The 'you' that I eat will be a softer version of what the snakes do, while once my body adapts, we can use your slime like the toads use their oil."
"Exactly!" Katsuyu nodded happily to see that her contractor understood it so quickly. "In fact, both methods were plagiarized from me in the first place, so they're not as safe."
This made Takara ponder a doubt.
"Is it possible that Tsunade didn't want to learn the sage mode because she would have to swallow a live slug?" he reflected, feeling enlightened.
"How much do you usually eat?" Katsuyu abruptly asked, snapping him out of his enlightenment.
"I don't know, a normal meal. Is that relevant?"
"This first step can only be done once and no more, so the bigger the 'me' you eat, the more effective the effect will be after digestion. So we need to calculate the size of your stomach and trachea to maximize as much as possible without choking," Katsuyu said seriously.
"So, can't I just cut open my stomach and let your clone enter?" Takara proposed as if it were obvious. "Then you can heal the wound, this way we can 'maximize' better, don't you think?"
Katsuyu looked wordlessly at her contractor, not expecting him to be so ruthless.
The worst part was that he was right!"