It didn't hurt anymore. In fact, it felt completely smooth. Kyoujurou stood up naturally and bounced on his feet a few times. There was no discomfort at all! Kyoujurou's big eyes widened even further. He was completely shaken. Could Su Chen really be a doctor, too? he wondered. His medical skills are amazing!
Seeing this, Kanao's face lit up with a small smile. She loved seeing people's reactions after Su Chen healed them. Every time Su Chen received praise, she felt even happier than when her own swordsmanship improved.
"Thank you so much, Mr. Su Chen!" the Rengoku brothers said at the same time. Kyoujurou couldn't believe that the leg ailment that had bothered him for years was fixed so easily by Su Chen. He suddenly remembered when Su Chen made that bet with Shinazugawa. At the time, Su Chen had boasted that he would defeat the Wind Hashira in just half a month. Kyoujurou had thought it was just a young man's way of motivating himself. But now... it seemed like Su Chen might actually have a chance to do it.
Facing their praise, Su Chen smiled faintly. "It's no trouble. But you'll still need to come to the Butterfly Mansion for one more treatment to fully recover, Big Brother Rengoku." Hearing this, Senjuro puffed out his chest. "Leave it to me! Big Brother Su Chen, don't worry, I'll make sure my Big Brother gets there, even if I have to carry him!" Kyoujurou fondly stroked Senjuro's head.
Su Chen spoke again. "This problem is actually caused by how you use your leg muscles, Big Brother Rengoku. If you can change your exertion technique, this kind of thing shouldn't happen again."
"Huh?" Senjuro was stunned. He had expected Su Chen to say many things, but he never thought he would question his big brother. His brother was a Hashira! Every move his brother made was like a template for other Demon Slayers. They were textbook movements! Besides, the Rengoku family's sword techniques had been passed down for generations. There was no such thing as an "incorrect technique"! Big Brother Su Chen must be wrong, Senjuro thought to himself. He was sure that his brother's injury must have come from a demon during a fight, and Su Chen had just made a mistake.
But Kyoujurou, as the Flame Hashira, didn't think so. He knew his family's history better than Senjuro. He knew that all the main Breathing Styles evolved from one original style. Flame, Stone, Wind, Water, and Thunder—these five basic styles were all created to fit different human bodies and habits. If Breathing Styles were made for imperfect people, why couldn't they be improved? Kyoujurou became more and more curious about what Su Chen would say next. With Su Chen's sharp insight, maybe he really had seen a problem during their spar.
The Rengoku brothers had different opinions, but they both watched Su Chen attentively. Kanao also looked at Su Chen, waiting for his next words. Under their gaze, Su Chen spoke. "Big Brother Rengoku, when you use your high-speed explosive sword moves, do your legs hurt?" Kyoujurou lowered his head and thought for a moment. Then he nodded. When he used 'Unknowing Fire' and other moves based on it, his legs did feel pain. He had always thought that was just a sign of using his full strength, so he never paid much attention to it.
But Su Chen's next words made Kyoujurou realize something. "When a person uses their legs, it's not supposed to hurt. If you feel pain, it means the movement is damaging your body. The body is sending you a 'warning'." "No," Senjuro immediately argued. "My brother was injured by a demon before! The pain is probably just an old injury, who knows?" "No, I can tell if it's an old injury or not just by looking," Su Chen said, shaking his head. He turned to Senjuro. "Do you really think any demon, other than an Upper Rank, could even harm Big Brother Rengoku? Let alone injure him so badly that it leaves a chronic problem?"
The Rengoku brothers were both stunned. They felt that Su Chen's words made a lot of sense. They listened carefully as Su Chen continued. "Therefore," Su Chen concluded, "your injury was self-inflicted." Kyoujurou nodded slowly and had to ask, "Then, Mr. Su Chen, is there a solution?" "Yes," Su Chen said, turning to him. "But first, you must demonstrate the Flame Breathing, Ninth Form, for me." Kyoujurou immediately understood. "Flame Breathing, Ninth Form - Rengoku?" Su Chen nodded. "Yes. I need to observe your complete Flame Breathing technique. Only then can I find the problem points in it."
Senjuro was stunned again. He didn't dislike Su Chen anymore, but he really didn't like what he just said. Find problems with Flame Breathing? If his brother agreed to this, wouldn't that be admitting that Flame Breathing has flaws? His brother would never agree to that! Indeed, Kyoujurou thought for a moment after hearing Su Chen's words. Then he asked, "Do I not need to demonstrate anything else?" "No need," Su Chen said slowly. "I've already memorized the other forms." "Memorized?" Both Rengoku brothers looked shocked. Did "memorized" mean what they thought it meant?
Su Chen repeated himself. "I've memorized all the movements you demonstrated earlier, and that includes your Flame Breathing technique." After speaking, Su Chen swiftly drew his Nichirin Sword. He was going to demonstrate it right in front of Kyoujurou. "Flame Breathing, First Form - Unknowing Fire!" A brilliant arc of flame bloomed in the air. Su Chen's movements were almost identical to the ones Kyoujurou had just shown! But there was a difference. Su Chen did not pour all his strength into his feet at once like the Flame Hashira did. Doing that would force too much blood into his feet and wear down the muscles over time. Instead, Kyoujurou watched as Su Chen used a method of high-speed body vibration to increase his speed. "Such fast draw speed," Kyoujurou couldn't help but praise.
Now the Rengoku brothers were truly speechless. They were convinced: Su Chen had learned the first few forms of Flame Breathing just by watching. Such terrifying talent! Kyoujurou had just been thinking about teaching Su Chen the style himself. It turned out he had already learned it on his own. This made Kyoujurou almost want to find a hole to crawl into.
"So, how about it, Big Brother Rengoku?" Su Chen asked again. "As long as you demonstrate the Ninth Form - Rengoku, I can figure out the problem with your legs based on how the technique works." Kyoujurou fell into hesitation.