Ding! Congratulations for reaching I-Cup! Accept rewards?
"Not so fast!" Sakura whispered, glancing over her shoulder to make sure nobody was eavesdropping on her. "I don't want to accept a reward and then wake up the next morning with a second pair of breasts; so, tell me what the prize is before I accept!"
The reward is half a Kakashi's worth of chakra. The Host will receive the same reward for each subsequent cup size increase, as a repeatable quest.
"That's it?" asked Sakura, feeling oddly disappointed. "Not even a full KK? And no more weird abilities?"
The System update introduced the Continuous Improvement feature as an extension of the Bounty feature that was present in the alpha version of the System. The Host can obtain more 'weird abilities,' as the Host puts it, but the Host will have to seek out bounty targets in order to obtain them.
In other words, the System's trial period was over, but that was a good thing, overall— lump increases in chakra would benefit her more than strange and often useless abilities.
Host! Continue hunting down the breasts of powerful and busty kunoichi to unlock hybrid abilities from the world of shinobi and the world of breasts! Learn these kunoichi's skills and fulfil additional requirements to learn and master these unique abilities!
Since Sakura's template originated from a rather low-fantasy world, the skills she had already obtained from the System had been slightly tweaked to be of use to her, so this was the natural progression of things, really. She would only be getting stronger and more useful skills from now on, but she would have to work harder to get them!
Even though Sakura had relatively large amounts of chakra compared to the average Genin, Chūnin, or even Jōnin, she could at most be considered to have reached the Special Jōnin level. She was extremely versatile and had an enormous volume of chakra compared to the average Jōnin, but she had yet to reach true mastery in anything but Genjutsu and chakra control, and most of all, she was still terribly inexperienced— although, mastering unique Jutsu would help counterbalance her immaturity…
From the bounty target Senju Tsunade, the Host can learn the Breast Seal ability: an upgraded version of the Yin Seal, which can hold any type of the Host's own chakra, such as elemental chakra and even Senjutsu chakra.
Learning requirements: a minimum of a 106 cm bustline and mastery of the Yin Seal Jutsu.
Sakura hadn't quite reached that level yet. However, she was still young, and her ribcage hadn't fully developed yet— which meant that her bustline would keep increasing by itself as she continued ageing, even if her breasts didn't grow any further.
"What can you tell me about the rewards I'll obtain from Samui?" Sakura queried. "I'm heading to the Hidden Cloud next, so I suppose she's next on the list."
The specifics will depend on Samui herself, but the resulting resentment generated from the severance of her breasts will most likely result in the birth of a type of Jujutsu— a cursed technique based on a certain taboo Manyuu Hiden Jutsu.
Learning requirements: obtain Hidan's triple-bladed scythe and obtain at least five deep-seated grudges born from taking away their breasts. Current count: 1/5.
'Sounds pretty evil to me,' said Inner Sakura hesitantly. 'I don't know if it would be a good idea to learn this one…'
"You know, what would really be nice is the ability to turn men into women," said Sakura thoughtfully. "There's only three or four Uchiha left in existence, and they're all men, so there's no way for me to obtain the Sharingan...."
Of course, there was always the option of waiting twenty years for her future daughter Sarada to come of age, but Sakura could hardly afford to wait that long— not to mention how messed up it would be for her to steal her own daughter's breasts.
…
At any rate, Sakura did not actually need to wait for her daughter to be born in order to obtain the Sharingan. There was a certain girl by the name of Uchiha Hikari who possessed a Mangekyō Sharingan who was still alive and well. Indeed, she had survived the Uchiha purge— by virtue of not having been present at the massacre to begin with, since she had got herself sealed away underground by the Senju and the Sarutobi clans a century ago.
But the only problem with harvesting her was that in this era, Tenten was the only one who even knew about her— Sakura didn't even know she existed!
…
Beep! Computing… Calculations complete! The Yin-Yang Gender Reversal Jutsu has been derived!
Requirements: Mitarashi Anko's breast chakra, any Aburame clan member's breast chakra, the Kaeru Kaeru no Jutsu, full mastery of Ying-Yang Style, Perfect Sage Mode/Philosopher's Mode.
"That's some shopping list," Sakura sighed. "And ugh, I'll have to deal with the bug users…"
Anko was a Jōnin, not to mention a comrade from the Leaf— getting her breast chakra sounded like it could prove quite an ordeal. Maybe if Sakura could get her drunk, or something…
Aburame clan members were all sensors by default, and their insects were pretty much immune to the Kurama clan's Kekkei Genkai, so getting the drop on any of them sounded like it would be difficult as well.
As for the last three requirements…
The Kaeru Kaeru no Jutsu was fairly self-explanatory, but even though Sakura had never heard of it, she had an inkling of who she could learn it from: Jiraiya.
Yin-Yang Style was some endgame-level stuff; it was something you'd automatically obtain upon reaching the Six-Paths level. That's not to say it was impossible to learn before then, since Madara had taught Obito how to use Yin-Yang Style— the problem was that Obito probably wouldn't be inclined to teach her in turn.
Sage Mode was a bit easier, though— in fact, Sakura could get started right now. She had absorbed a sliver of natural energy from Tayuya's Cursed Seal along with her chakra, so if she isolated it, and used it as a reference to sense the natural energy around her…
BEEP! WARNING!
Insufficient chakra levels! If the Host persists in trying to absorb natural energy, the Host will turn into a stone statue! The minimum amount of chakra required to reach the Sage Mode's introductory level is 7 KK!
Sakura froze; she had almost made a mistake from which there was no return!
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It's the busty kunoichi teacher Sakura's Maths class!
We already know that Shippuden Naruto has four times as much chakra in his base form than Kakashi, and thanks to the Databooks (which really aren't trustworthy), we know that Shippuden Naruto scores a 5 in Stamina, while all versions of Kakashi score a 3 in Stamina.
Then, taking into account that Chūnin exams Sasuke can perform the Chidori (which costs 0.25 KK to cast) twice, and that this version of Sasuke scores a 2 in Stamina, we can guess that each of the Databook's ranks has around at least 2.5 times as much chakra than the previous rank.
Rank 1: 0.15 KK — 0.39 KK (Chapter 1 Sakura)
Rank 2: 0.40 KK — 0.99KK (Chapter 1 Sasuke)
Rank 3: 1.00 KK — 2.49 KK (Kakashi has exactly 1 KK, Third Hokage)
(Orochimaru inhabiting a nobody's body is between Rank 3 and 4)
Rank 4: 2.50 KK — 6.49 KK (Chapter 1 Naruto, Tsunade)
Rank 5: 6.50 KK and beyond (Jiraiya, Minato, Shippuden Naruto)