"Swastika: Residual Fire Sword"
When Kaoru Tsubasa saw that the torch he'd just unleashed had no effect on Garp's black energy, he immediately activated his Bankai.
Boom—
A tremendous column of flame shot into the sky and then retracted, coiling back into the blade of the Zanka no Tachi.
After Kaoru released his Bankai, the surrounding ocean evaporated outright; the water of the Redoria Sea vanished. Even the fish on the seabed died where they swam. Farther afield, places grew hot to an almost unbearable degree.
At Navy Headquarters, Kuzan felt the sudden spike in temperature and frowned. He tried to bring his ice down to counter it, but found his powers strangely impaired.
"What in the world…?" Sakazuki muttered, feeling the air itself burn. His magma felt weak in the face of that heat.
"It's horrifying—like facing the sun itself," Borsalino complained idly as he cut his nails.
Sengoku, too, felt the temperature change and paused in alarm.
Aboard the Moby Dick, Marco reeled at the reading, while Whitebeard's hand tightened around a bottle. Newgate's mind flicked to Kaoru—if anyone could do this, it was him.
In Wano, Buggy and Kaido both felt the terrifying heat. Buggy, who'd absorbed the Grace of the Sun, knew how lethal that kind of temperature could be; he had never felt anything like it.
Outside the Redoria Sea, Kaoru slashed.
"Zanka no Tachi — North: Ruin of Heaven and Earth."
His blade cut through Garp's black energy. Where the sword met the darkness, the attack vanished as if it had never been. Garp stared in disbelief—his full-strength blow, the one he'd practiced toward perfection, had been erased by a single strike.
Kaoru ignored Garp's shock and fully released the Zanka no Tachi's form. The coastline of Redoria itself dropped hundreds of meters in less than a minute—Kaoru had not mastered the blade yet; the scale of the power was partly uncontrolled.
Garp, pursuing on moon-steps, landed on the shore and asked, breathless, "Boy—what was that heat just now?"
He'd been too focused in the fight earlier to take it in, but now the memory of that temperature chilled him more than any breeze. Even armament Haki might be consumed by it.
"That's the power of my sword," Kaoru said, and presented the blade: Ryujin Jakka, its edge still warming the air.
Garp examined it. "Is that… one of the Twelve Supreme Swords?"
Kaoru shook his head. "No. It can rival the Twelve, but it's not categorized the same way."
Garp's brow furrowed; though not a swordsman himself, he'd encountered many famed blades and recognized the aura. "So it's not in the usual list… Huh."
"Anyway, what brings you here, Garp?" Kaoru asked, though he roughly guessed.
Garp snorted and picked his nose. "Didn't that masked fellow tell you? I came to see Luju's grave."
Kaoru led Garp to the temporary grave he'd prepared. When the masked man on Baterilla Island had told Garp that Luju's body would be buried in Redoria, Kaoru had built a fake grave here—while the real bodies of Luju and Roger lay safe in Kaoru's system space.
Garp inspected the tomb and found nothing unusual; his observation Haki detected no deception. Kaoru had placed a decoy in the mound that simulated the presence of a corpse perfectly. Satisfied, Garp left.
Back at the cabin, Kaoru found Nico Olvia (Olbia) writing in a corner. She had been making records—notes and sketches salvaged from O'Hara—because now, with few survivors, the task of passing that knowledge on fell to her.
"Were you fighting earlier?" she asked. Even from inside the house she'd felt the aftershocks: the sudden rise in temperature, the singeing gust at the edge of the woods.
Kaoru nodded. "Vice Admiral Garp came by, but he's gone now."
Olvia stiffened—Garp, the heroic old man of the Navy? But she regained composure quickly. Kaoru was not a man to be easily bested; if he could stand in Redoria, he could stand against most threats.
Kaoru, for his part, was relieved Olvia had stayed behind. Given the Navy's attitudes, any tie to O'Hara could have been dangerous; it was better she remained hidden.
There were plans ahead. A number of events would shape the sea over the next decades. Luffy would be born in three years—there was time, but the system's mission demanded Kaoru act carefully. He had twenty years to influence the major turns that would come.