In the field of sealing arts, Dan shifted his focus toward intensive research and a deeper level of study. Through constant experimentation, he successfully unlocked the path to the next enhanced stage of the Vitality Seal, further securing his journey toward longevity. Theoretically, this advancement wasn't overly difficult for him, simply because the concept had existed in his mind as part of his holistic vision from the very beginning.

  The path of the Vitality Seal, with its various stages, had been roughly mapped out in Dan's mind since the start. He knew the general trajectory and the expected goals of each phase. All he truly needed at this stage was to understand how to translate these theoretical ideas into a safe, practical, and effective application on his own body—a task that required time and effort but was far from impossible after his initial successes.

  Looking back at the previous stages he had already applied to himself and his wives, the foundational first step focused primarily on the skeletal system, specifically the bone marrow. The marrow is crucial as it produces the blood that circulates through the body, nourishing every cell and organ. The core idea of that stage was to seal chakra into the bones to feed the marrow, which in turn produced blood saturated with healing chakra.

  The next enhanced level, which Dan applied to himself years ago, targeted the muscles directly rather than relying solely on blood circulation. This massively increased muscular vitality, strength, endurance, and recovery. This level boosted his projected lifespan to approximately 350 years—a significant span, yet still short of Dan’s ultimate ambition.

  The level he is currently developing is far more delicate and dangerous. It focuses on directly nourishing the internal organs and viscera through the seal—vital components like the heart, liver, kidneys, lungs, and stomach. Theoretically, the principle is the same: if he could successfully nourish bone and muscle, he should be able to do the same for organs. However, in practice, the risks are exponentially higher.

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  The primary difficulty lies in the extreme sensitivity of internal organs compared to dense bone or flexible muscle. A single slip or minor error in applying the seal to such sensitive tissue could be fatal, potentially stopping his heart instantly. Consequently, Dan took much longer than usual to plan every detail, conducting numerous experiments on various animals to test methods, observe failures, and identify potential risks.

  Recently, after a long period of meticulous trials and constant adjustments, he finally found a relatively safe and effective method. The idea is innovative: he will extend the existing seals in his bones and muscles—which are already interconnected in a complex network—and then use his thread technique to form a micro-web around each sensitive internal organ. This web acts as a protective and nourishing envelope.

  These chakra threads serve as flexible, mobile seals that are easier to manage than tattooing inscriptions directly onto pulsating organs like the heart or lungs. By connecting these micro-webs to the established skeletal and muscular seals, the entire system functions as a single, integrated unit. This technique requires a level of chakra control so precise that most people cannot even fathom it.

  For Dan, however, this was achievable. His Kekkei Genkai provided the necessary control, his massive reserves ensured the system could be maintained without exhaustion, and his years of mastery over the thread technique made the impossible seem practical. Based on his calculations, he expects this advanced version of the Vitality Seal to extend his lifespan to roughly 500 years—half a millennium of life.

  While 500 years is not yet true immortality, it is a massive stride in the right direction. Dan is confident that with this extra time, he can develop even higher tiers targeting the nervous system, the brain, and eventually, direct cellular-level manipulation.

  In his lab that night, he reviewed his detailed diagrams one last time, checking every minute stroke of the new seal. He prepared himself mentally and physically for the dangerous procedure. He knew the risks, but he trusted his preparations and his skills. Looking toward the next five centuries, he felt his power would only continue to grow. He smiled a faint, confident smile; longevity was drawing closer, step by step, day by day.