The power to cross space and time, and "It"

Taking a drag, the old man opened his mouth and let smoke drift from its corners. "I'm a Devil Fruit user who ate a Mythical Zoan, Model: Mountain Lord."

"This fruit not only lets me control the souls of the dead, copy abilities displayed by other Devil Fruits, and construct illusions through my eyes, but also grants me one chance to open the Gate of the Underworld after awakening."

"Although I don't know exactly what the world beyond that gate looks like, I do know it's the world of the dead, and I..."

"Can plunge this island into the true Underworld."

At that, he straightened his back and stared into Kuta's eyes, his gaze cold. "Although I'll certainly die afterward, and I believe you might escape, the people on this island—and those companions of yours—might not be so lucky."

"Are you threatening me?"

Kuta frowned slightly, staring at Carteles as anger flashed in his eyes.

He

didn't know whether the man was telling the truth, but as for the Underworld, he knew it apparently really did exist in this world.

Brook had eaten the Revive-Revive Fruit, which allowed his soul to return from the Underworld after death and come back to life.

The Underworld.

Should I let this guy go?

He stared at Carteles, an overwhelming killing intent erupting from him. He wanted to kill the man, but he didn't want to risk his companions' lives. He didn't know whether he could really handle the unknown Underworld. After all, it involved souls.

But he couldn't stomach letting the man leave, either.

No one knew whether the old man spreading information about him would send the World Government into a frenzy.

He wouldn't be in much danger himself, but the danger to those around him would increase dramatically.

Even Isshin Dojo