Observation Haki was not an all-purpose scanner.
Although Observation Haki, when trained to its peak, could foresee the future, it could not sense everything unless it was actively used.
How had Red-Hair lost his arm?
Why, in the original story, had Whirlpool Spider been able to stab straight through Whitebeard's heart?
Why had Blackbeard and his group gone undiscovered by the Marines for so long after arriving at Marineford during the Summit War?
The reason was simple. Observation Haki could not remain active at all times, nor could it passively sense everything as people imagined.
Two Compressed Explosive Rock Bombs suddenly flashed with blinding light.
The Explosive Rock Bomb Whitebeard had thrown was swallowed whole by Saint Peter using his old method. Then, a massive magic circle suddenly appeared beneath his enormous body.
The purple-black magic circle crackled with black lightning and black flames.
The giant insect that had swallowed the Compressed Explosive Rock Bomb flickered, then abruptly vanished from Mary Geoise.
The sudden turn of events left the Marines, who had been preparing to dodge, stunned.
As for the Dyna Stone Roy had activated, it was too far away. Aside from Saint Saturn drawing upon the remaining power of Mary Geoise's protective barrier to erect another shield—
Darkness suddenly spread from the direction of Pangaea Castle, shrouding the area where the explosion was about to occur.
At the same time, the other Five Elders and the Marines who had just climbed onto the Red Line Continent could only use their bodies and Devil Fruit powers to protect Pangaea Castle and the Celestial Dragons near them.
Just as everyone on Mary Geoise focused their attention on the Dyna Stone bomb that was about to explode—
Roy, Whitebeard, and Kaido had already pushed themselves to the limit and reached the skies