Given the current urgent situation, where every minute and every second carries the risk of world destruction, there is no time to hesitate and devise a more thorough plan; action must be taken immediately.
Considering the monsters at hand, Shiranui has completely filled the surface, and attacking it would only cause the flesh to grow more profusely, making it very difficult to physically create a passage in a short time to enter the underground spirit vein and seize the Holy Grail.
So, Li Pan made a decision on the spot: take a shortcut! Go through the backdoor! Get the key!
Aqi used a silver key to open a door that led directly to the underground cells of Chiyoda Prison, likely where the felons were detained. It must be said that these cells were sturdy, having survived two nuclear blasts and continued bombardment for so long without collapsing. Their solidity was comparable to Li Pan's own, which is why Kotaro could never escape in the past...
