Techniques for absorbing chakra were indeed rare, but they were hardly anything extraordinary. Nor did they require the Rinnegan's Preta Path ability to achieve.
Orochimaru's subordinate, Yoroi Akado, possessed this very trick. In the original timeline, he had clung to Sasuke while he was suffering from the Cursed Seal and drained him to his heart's content.
However, if "chakra absorption" were ranked into different tiers—
Yoroi Akado's method could only absorb chakra through direct physical contact. Moreover, his ability to adjust the frequency of foreign chakra and synchronize it with his own was poor, resulting in extremely low absorption and fusion efficiency. More than seventy or eighty percent of the chakra he absorbed could only go to waste—without question, it was the lowest tier.
The resurrected Madara Uchiha had no Rinnegan, yet he could step on Allied Shinobi Forces ninjas and absorb the Nine-Tails' chakra, or seize the First Hokage's neck and steal Sage Chakra. And judging by Madara's condition after absorbing chakra, his absorption efficiency was remarkably high, nearly one hundred percent. His mastery was clearly on an entirely different level.
But even Madara Uchiha, whose mastery of this "Star-Absorbing Technique" was so profound, could not absorb an opponent's chakra anytime and anywhere while fighting them.
Kisame Hoshigaki could.
Kisame Hoshigaki, who often fused with Samehada, seemed to have acquired Samehada's inhumanly absurd chakra-absorbing ability. Even in the midst of intense combat, as long as an enemy's chakra came into contact with him, he could instantly seize it and make full use of it to replenish his own expenditure. Even chakra with sealing properties and powerful suppressive force was something his shark-like teeth would swallow without hesitation.
Yoroi Akado level, eyeless Madara level, Kisame level.
Above those was, naturally, the power of the Rinnegan. The Rinnegan was, after all,