When Orochimaru and Kabuto Yakushi entered the laboratory to see Sasuke, they were surprised to find Sasuke conducting experiments on Kimimaro.
The sight startled Orochimaru, who feared Sasuke might harm Kimimaro. However, upon closer inspection, Orochimaru realized the situation differed from his initial assumptions. Sasuke noticed Orochimaru's arrival and greeted him casually, "Orochimaru, you're here."
Orochimaru, instead of responding, focused intently on Kimimaro's body. He then glanced at the instrument beside him, where the screen displayed information on Kimimaro's physical condition. The data clearly showed that Kimimaro's health had not only returned to normal but also had significantly improved. Originally, Kimimaro's physical fitness was excellent, but now it had reached a level akin to the first stage of the curse seal.
This revelation puzzled and excited Orochimaru. He looked at Sasuke with a mixture of doubt and anticipation, eager to understand the reason behind Kimimaro's remarkable transformation. "Sasuke, how did you manage this? Why has Kimimaro's condition improved so dramatically?" Orochimaru's voice was filled with curiosity and surprise. "I didn't have a solution for Kimimaro, yet you resolved it so swiftly."
Orochimaru admired Sasuke's abilities and was eager to learn more. Sasuke, with a slight smile, replied, "It's not difficult. Kimimaro's blood disease was primarily due to the use of his Shikotsumyaku, which brought bacteria from the air into his body. Although these bacteria aren't harmful to most, in Kimimaro, they attached to his bones and caused his cells to die. The more he used his Shikotsumyaku, the worse his condition became, leading to his eventual demise. The solution was simple: strengthen Kimimaro's cells to a point where they were unaffected."
Sasuke's tone was confident and assured, as if the solution was obvious. "You, the creator of the Curse Seal of Heaven and Earth, should understand this." Sasuke's words were tinged with ridicule, expressing his disappointment with Orochimaru's lack of understanding. "I'm disappointed in you."
Sasuke's contemptuous gaze made Orochimaru feel inadequate. Orochimaru, however, masked his feelings and continued to inquire about Sasuke's methods. He believed that Sasuke might have discovered a technique to strengthen cells and cure blood diseases, which could be invaluable for his research.
Suppressing his dissatisfaction, Orochimaru gently asked, "Please, tell me how you did it." His voice was sincere and filled with anticipation. Sasuke, with a light smile, responded, "You really want to know?" Orochimaru nodded eagerly, intrigued by Sasuke's capability to enhance Kimimaro's cells.
However, Sasuke laughed and said, "Sure, but only if you swear loyalty to me." Orochimaru, although expecting such a demand, felt conflicted. Sasuke then added, "Oh, by the way, the state of one's cells determines lifespan. In theory, upgrading a person's cells to a certain level could lead to immortality."
These words deeply moved Orochimaru. Eternal life was his ultimate pursuit. Combining this with his passion for research made the prospect irresistible. "There's only one answer," Orochimaru declared. "I pledge my loyalty to you!" He drew his Kusanagi sword, ready to demonstrate his commitment, but Sasuke stopped him.
"Alright, no need for theatrics. Just serve me well, and I promise you immortality." Orochimaru, putting away his sword, looked at Sasuke with a smile. "Then, Lord Sasuke, can you teach me your method now?" His tone was filled with eagerness.
Sasuke approached Kimimaro and explained, "The Shikotsumyaku bloodline won't cause side effects if the user's physique is strong enough. Kimimaro's body, though robust, isn't on par with the Senju or Uzumaki clans. I developed a new seal, based on the Curse Seal of Earth, and named it the Blood Seal."
Orochimaru, confused, asked, "The Blood Seal? How is it different from my Heaven and Earth Curse Seal?" Although the names sounded similar, Orochimaru doubted their effects were the same.
"The Blood Seal enhances the user's constitution based on their physical condition. For instance, if Kimimaro's blood disease stemmed from his physical limitations, the Blood Seal would bolster his physique to the point of disease immunity. That's why Kimimaro's condition has improved so much."
Though Sasuke had given Kimimaro the powerful Blood Seal, he also employed some "tricks" to ensure its effectiveness.