Sasori of the Red Sand, having defected from Sunagakure, had likely been on a "whim of a journey" ever since, wandering the ninja world. However, even an S-rank puppet master considers his own safety; there are places he won't go recklessly.
Deep into the Land of Fire, for instance.
Even though they were currently near the border, the reality of the Great Ninja War meant they weren't far from the front lines where Jiraiya, the Toad Sage, was stationed. Given Jiraiya's legendary strength and Sasori's own high-profile status as a traitor, Sasori had no desire to trigger a full-scale pursuit by an S-rank Konoha shinobi while his own "art" was in an imperfect state.
If Sasori had already completed his transition into a full human puppet—possessing a "Core of Living Flesh" and attaining "eternal" life—he wouldn't have retreated. He would have pursued Ui with the single-minded obsession of a perfectionist hunting premium materials.
But as fate (and bad luck) would have it, Sasori found his "Strongest Puppet," the Third Kazekage, rendered useless by the Magnet Style "expert" Uwabami Ui. With his ultimate technique, the Performance of a Hundred Puppets, still incomplete, Sasori was effectively fighting with only half his true strength.
Ui didn't know Sasori's exact internal monologue, but he breathed a sigh of relief when the pursuit ended. The pressure of an S-rank missing-nin is no joke. He had purposely led Sasori toward the Konoha front lines as a deterrent, betting that a rogue ninja would know better than to run into a nest of Leaf shinobi.
It worked.
The Analysis of the Railgun
Ui's goal from the start was survival, not a duel to the death. He hadn't even shown his full hand yet—Ui was the type to keep his absolute trump cards hidden until the literal moment of life or death, largely to maintain a psychological advantage.
As the rain washed away the mechanical clicking of the puppets, Sasori vanished, leaving behind only the splintered wreckage of his red-robed dolls. Notably, Sasori had kept his remaining puppets close until the very end, wary of Ui's final attack.
Sasori didn't know the name of that technique, but its speed, power, and destructive reach were impeccable. He estimated its effective range at about 50 meters.
To put it in perspective: Sasori had seen Tailed Beast Bombs. Compared to the Railgun, a Tailed Beast Bomb has more raw destructive energy and a range of 1000+; it's a strategic weapon meant for leveling villages.
Ui's Railgun, limited by current output, was a precision anti-personnel weapon. Max targets: 1. Max range: 50m. But in terms of quality? It was easily Rank A++.
If a Tailed Beast Bomb is a sledgehammer, the Railgun is a needle-sharp rapier. If it hits, it doesn't matter who you are—even if you brought the First Hokage out of his grave, you'd have to wonder if his legendary healing could outpace a hole being punched through his chest at Mach 7.
Of course, a move is only "broken" if it hits. Tailed Beast Bombs are terrifying, yet statistically, they've probably killed fewer named characters than the "Rasengan" blue-pill family line. Sometimes, a well-timed kunai is more effective than a flashy ultimate.
Reunion at the Base
Once certain Sasori was gone, Ui began the trek back to the rendezvous point. Despite the hours lost in battle, he suspected his team hadn't left yet. With Asuma's injuries and the chaos of the Land of Rain, the safest bet was to stay hidden in their secret tree-hollow base.
After a few hours of navigating the downpour, Ui reached the coordinate. He didn't just walk in; he pressed his fingers to his lips and let out a sharp, melodic whistle—the pre-arranged signal.
A matching whistle echoed from the hidden entrance.
Ui relaxed. He pulled back the camouflaged covering of the tree hollow. Yuhi Kurenai, Sarutobi Asuma, and Yamashiro Aoba were all there, looking like they'd seen a ghost.
Ui looked a bit worse for wear, and his "silhouette" had changed—he was now a "Gourd Brother," specifically the Black Gourd. But he was alive, which was more than they had dared to hope for after he'd stayed behind to face the Red Sand.
"I have major intelligence," Ui said before they could even start the interrogation. "We need to report to headquarters immediately. We move now."
He glanced at Asuma, whose wounds had been freshly tended to. Again.
"Yamashiro, carry Asuma. Let's go."
Aoba nodded and hoisted Asuma up somewhat roughly. Asuma winced as his wounds were jostled. If he'd had his way, he would have preferred Kurenai to do the carrying, but alas—even in his fantasies, the world wasn't that kind.
The team is moving through the rainy woods, heading for the Konoha border. Ui is carrying the heavy Iron Sand gourd, while the group processes the fact that they survived an S-rank encounter.