At the baseline, Mitsuya held up a tennis ball and looked across at Inui Sadaharu. He served at a slightly reduced speed. As the ball cleared the net, Inui rushed to the landing spot and returned it. Watching Mitsuya's movements, he began running to the right while saying:
"Based on your habits in the first three games, senpai's return shot to the…"
"To the crosscourt side has a probability of 84%, is that what you were going to say?" Mitsuya interrupted before Inui could finish.
"Wh-what?!" Inui's face twisted in shock.
But before he could process it, Mitsuya's return was already flying toward him. Just as predicted—a crosscourt shot. Yet Inui felt no sense of triumph. He had no idea how the opponent knew his calculations.
He quickly returned the ball and resumed his predictive play, saying:
"Retreating to the backcourt has a 91% probability, and the down-the-li—"
"Down-the-line shot is at 87% probability, right? Isn't that correct, adorable kouhai~?" Mitsuya smiled again and cut him off.
That sealed it—Inui was sure now. This opponent was also a data tennis specialist. But during his pre-match research, he'd found nothing about it. How was that possible?
"You must be wondering why you didn't find anything about me playing data tennis," Mitsuya said calmly, reading Inui's expression.
Inui kept running and returning shots, but his heart was in turmoil. 'Has every move of mine already been calculated?'
"Your data tennis was taught by Renji, right? I always told Renji that information is a weapon. And if it's a weapon, doesn't it make sense to keep it disguised?" Mitsuya continued to smile as he spoke.
"Senpai, you know Renji?" Now Inui wasn't just surprised—he was curious.
"Oh? Didn't Renji tell you? I'm the one who taught him data tennis," Mitsuya said casually. Then he slammed a fast drive, catching Inui off guard and winning the point.
"15-0!"
"So that's how it is…" Inui was totally thrown off by the revelations and no longer knew what to think.
Not just Inui—everyone watching, including Fuji and the rest, were equally shocked. No one had expected Inui's opponent to also be a data tennis expert. And from the look of it, Inui's style of data tennis actually originated with Mitsuya. There were no words.
"Looks like Inui is in real trouble this time. If it's a battle of data tennis, he has no chance. And purely in tennis skills… let's not even go there," Fuji said, face tense.
Besides Kawamura, who had gone with Yamato to the hospital, Oishi and Kikumaru also looked worried. But none of them could do anything. Data tennis was outside their wheelhouse—this was entirely up to Inui now.
"Now that you know your data might be useless, what will you do, kouhai~?" Mitsuya's gentle tone made Inui's whole body break into a cold sweat.
"Don't know what to do? Then I'll give you two options. One, keep using the data you've gathered so far, and adjust as the match goes on. Or two, abandon the data and rely on instinct to try to win. Which will you choose?" Mitsuya asked, watching the troubled look on Inui's face.
Inui hesitated. Should he really abandon data? But without it, he'd have no chance. Yet clearly, the data was failing him now.
The umpire called for Mitsuya to serve, but he ignored it, watching Inui with amused interest, waiting for his decision.
"Time violation! Fault! Second serve, please!"
The umpire's call jolted Inui from his thoughts. He looked up and saw Mitsuya still standing there, waiting. Gritting his teeth, Inui said:
"Senpai, if I give up data, I have nothing left. Even if I know the data's wrong, I can only rely on it to play. Because this is my path in tennis!"
Mitsuya smiled brightly, pleased by the answer. He was truly happy. Even cornered like this, Inui hadn't abandoned his style. In that case, Mitsuya would teach him what real data tennis looked like.
"Very well. Then keep walking your path. I'll show you what data tennis truly means. Be ready, kouhai~" Mitsuya said, and under the umpire's urging, served the ball.
"Foot position half a step ahead on the centerline, net approach probability 73%, drop shot probability 81%, correction value 7%!" Inui chanted aloud as the stream of data flew from his lips.
As Inui Sadaharu rushed toward the net, Mitsuya moved forward just as predicted. But then he calmly spoke up:
"Probability that I'd approach the net: 91%. Probability that I'd use a drop shot: 87%~" As he said this, Mitsuya returned the incoming ball with a clean down-the-line shot.
"Just as expected. The opponent calculated my prediction, which means the probability he'd switch from a drop shot to a down-the-line shot is 94%!" Inui didn't look surprised by the change but adjusted his swing mid-run to match.
Just as the ball was about to land and Inui was prepared to intercept, the ball suddenly took an odd deflection off the court. Caught off guard, Inui barely managed to get his racket on it, but the return was of very poor quality.
Watching the lobbed ball rise into the air, Mitsuya jumped and called out:
"Probability that I'd switch to a down-the-line shot: 95%. Probability of noticing a small stone on the ground: 2%. Probability of barely returning a lobbed ball: 90%. Probability this point ends in a score: 100%!"
With that, Mitsuya's smash landed hard in the back of Inui's court and shot out of bounds.
"30-0!"
After scoring, Mitsuya looked at Inui, who was staring blankly at the stone by his feet, and said:
"Data tennis isn't just about calculating the opponent's actions. You also need to collect data on the court and the environment. Build a 3D simulation model in your head to help analyze every possible variable~"
Inui slowly exhaled, bowed, and said:
"Thank you very much for the guidance, senpai."
"I told you, there's no need to thank me. Having a kouhai like you makes me happy. Now, let's continue~" Mitsuya waved his hand and smiled.
The match resumed. Inui kept refining the data he was collecting, this time also paying attention to ground conditions and wind speed—converting it all into data, constantly breaking it down and rebuilding it in his mind.
"Probability of aiming at the back corner: 83%. Correction value: 6%. Wind speed: 1.75 meters per second. Ball speed increase: 0.21%!" Inui mumbled nonstop.
"You're wrong. Crosscourt shot probability is 89%. Wind speed is 1.746. Your data correction still needs work, kouhai~" Mitsuya's calm voice rang out again.
"40-0!"
"Down-the-line shot probability: 91%. Correction value: 9%!"
"Wrong again. Underspin shot probability: 86%!"
"GAME! Yamabuki Middle School! 4-0!"
Inui continued collecting and recalculating data while Mitsuya kept correcting him, guiding him, pointing out each error in his calculations.
To outsiders, the match was incomprehensible. In the players' seats, Kikumaru's eyes had turned into swirls. Oishi was drenched in cold sweat, completely unable to keep up.
Even Fuji was frowning. He'd seen Inui's data tennis before and believed it could be avoided if you stayed sharp. But now, watching Mitsuya, he wasn't so confident anymore.
Fuji thought that in Mitsuya's eyes, he was probably completely transparent. If they played, all his movements and techniques would be instantly recorded and computed. It reminded him of his match against Akashi—being completely dominated, every move predicted. Could Akashi be using data tennis too?
But something didn't feel quite right. Akashi's presence was different from Mitsuya or Inui. There wasn't any visible complex calculation—just pure insight, as if he could see the future.
As Fuji's mind wandered through this mess of thoughts, the match on court continued. Even though Inui was pushing his mind to the limit, collecting and analyzing data at full capacity, he couldn't touch Mitsuya's level. It felt like a child facing an adult—no resistance at all.
"GAME! Yamabuki Middle School! 5-0!"
"15-0!"
"30-0!"
Only two points remained in the match. Inui hadn't given up yet and was still trying to break through Mitsuya's data lock, but he knew deep down it was useless.
At the baseline, Mitsuya prepared to serve again and spoke:
"You must've experienced it enough by now. Looks like your data handling has improved too. But what you've seen so far is just part of my data tennis. It's time I show you what real data tennis looks like."
Inui froze. What did he just hear? Real data tennis? Then what had they been playing all this time? Part of it? A thousand questions flooded his brain.
Mitsuya served again. Inui shoved those questions aside and focused on calculating and analyzing. But things didn't go as expected.
"Crosscourt shot probability… how can this be?! Unreadable?! Where's all this massive data in my head coming from?!" Inui felt like his brain was about to explode. Countless fragments of data surged in, forming an overwhelming data stream crashing into his mind.
"40-0!"
"GAME! 6-0! Match over! Winner, Yamabuki Middle School!"
As the match ended, Mitsuya walked over to the stunned Inui, who was holding his head. Standing before him, he said calmly:
"Every strike on the court generates countless data—air resistance, axis of spin, ball speed, racket face friction, even ball deformation. Add to that the opponent's skill, behavior prediction, court factors… and you get an infinite number of result branches. Just now, I converted all of them into data and hit you with a data stream assault."
"Kouhai, I'll leave you with one last tip. Data isn't just for collecting—it can also be input and output. Once you understand that, you'll have truly mastered data tennis. Keep at it!"