"Zzzip." The Flying Wheels spun rapidly ahead, slicing through the earth and carving out a passage for Gray to travel underground.
As he carved out a passage a hundred meters below the surface, Gray activated Observation Haki to sense nearby presences. He deliberately avoided the powerful members of the Beasts Pirates stationed in Wano Country, as well as the local strongmen.
For example, Queen, who often guarded Udon.
Hyogoro, who taught Luffy Ryuo.
And Ashura Doji, the bandit chief.
They were all fairly powerful. If Gray dug a passage beneath them, the commotion might draw their sharp attention. If they then activated Observation Haki, he'd be in trouble.
"Hmm! To be safe, I'll dig another hundred meters down. I remember that scene from my previous life—the underground space where the Road Poneglyph was kept was pretty big and deep!"
"Forget it. I'll go another hundred meters down, to three hundred meters underground, and search all of Wano Country. I refuse to believe I won't find it!" He controlled all four Flying Wheels at once. The dirt and rocks he dug up melted before they could even hit the ground.
A small amount turned to ash outright, while the larger, sturdier pieces left behind something like magma.
With Observation Haki to guide him, Gray had no fear of digging the same passage twice. And since his ability was so convenient, he carved his way forward as quickly as an ordinary person running at full speed.
The underground world was pitch-black, making it impossible to sense the passage of time. Without Observation Haki to guide him, Gray might have struggled even to walk.
As he dug, a clear, loud sound rang through the darkness.
"Gurgle! Gurgle."
"I'm hungry!"
"Can't be helped. I'll have to take a break and go find something to