Kanzaki Kaori's feet touched down on the upper surface of the giant structure.
It was Radiosonde Castle.
Its altitude was so great that there was nothing even remotely like clouds near it. Both above it and below it was a color halfway in between indigo and black. Much farther down, the familiar blue could be glimpsed.
The surface below her feet felt similar to stone. Radiosonde Castle was in the form of a giant cross and appeared to be made up of a jumbled assembly of multiple churches and temples. The styles of construction were all different, but the level of damage to the stones was all even. Everything was new.
Simply put, it seemed that a single type of material had been built up into that giant shape in order to look like it had been created from a collection of churches and temples from around the world.
"I have landed!! I am about to head down to the lowest level of Radiosonde Castle and begin interfering with the balloons as needed. Help me with the values and calculations!!"
Agnese's voice immediately reached Kanzaki's ear.
"Understood. Depending on its rate of descent, we will choose one of two target areas for it to fall either into the Indian Ocean or in the Pacific Ocean. First destroy just one of the balloons so we can determine just how much of its lift it'll lose. With some definite values from that, we can calculate a method from there."
On the bottom of Radiosonde Castle were over two hundred giant metal balloons. It was unlikely that destroying just one would cause the entire structure to suddenly fall.
Whether it was from the magic side or the science side, she had not yet noticed anyone onboard.
(…When I landed, I was not obstructed by any magic or anti-aircraft weaponry.)
However, she could not be sure, as Radiosonde Castle was simply too large. It was possible that some personnel were hidden elsewhere and they may have simply not used any magic or guns to intercept her.
She simply could not tell what they were thinking even after actually setting foot on that giant facility.
That made Kanzaki feel uneasy.
The staircase was similar to scaffolding at a construction site, but the actual materials making it up were the same as the rest of the temple's. It looked as if the walls had been twisted and forcibly made into stairs like a sugar sculpture.
"…We only have the records from long-distance observation to compare to, but it really does seem to be imitating the Star of Bethlehem."
"That served the function of modifying the flow of power on a global scale, so it was essentially a giant switching device. So is this one the same…?"
"But I can't discern any goals which would make sense for that. Really, it feels like a transformer with no electricity flowing through it. I can't imagine what important reason this thing could have."
"If its purpose isn't to float up there, maybe it's to be dropped on something?"
"Unless they just want the end of the world or something, I don't think anyone would want that kind of indiscriminate destruction."
Whether it was meant to float up there or drop down, she could not find any logical aim.
Of course, making a structure that large fly would require massive costs to prepare, carry out, and maintain.
That fact gave Kanzaki a bad feeling.
The small fact that she could not see what they were after invited in a great unease. It made her think that she was making a major misunderstanding.
"…I've arrived at the lowest level."
Kanzaki forcibly cut off her negative thoughts and focused on the situation in front of her.
The ceiling above was made of thick stone, and the blue sky could be seen far below her feet. Scenery she could never have seen on the surface spread out below her. The place she was standing in truly did seem to be based on construction scaffolding. She was on a passageway made of a narrow mesh that was hanging down from the stone ceiling.
It was similar to construction scaffolding in its form, but it was made of stone. Also, it did not seem like the people that had built it were thinking of safety standards at all. Kanzaki looked around while constantly paying attention to her footing.
She saw giant spherical tanks that were a few dozen meters across.
They were hanging down like fruit from the giant stone structure that was a few dozen kilometers across. As there was nothing else to compare their size to, the scene messed with her sense of scale.
"The method it uses to float is still unknown. If it does use some kind of gas, you need to keep in mind the possibility that it is flammable."
"The balloons themselves are large, but Radiosonde Castle is simply so huge that there is little risk of other balloons exploding if a flammable gas in one explodes." Kanzaki calmly analyzed the situation. "In fact, what would get caught up in the blast would be the scaffolding around the balloons. I would like to avoid leaving before all the work is done."
The metal balloons and the scaffolding were both hanging down from the giant stone structure above her head. She had no idea how far its effects would spread if an explosion did occur. It was even possible that the stone structure that seemed to cover the sky would separate, sending her crashing down.
Kanzaki made sure that she had a straight path to the nearest staircase up to a higher level, and reached for the sword hanging from her waist.
Technically, she was reaching for the seven thin wires stored on the sword's scabbard.
"I'm beginning. What is below me?"
"You are around the center of Eurasia. The area is complete wilderness. There are no civilian, military, or magical facilities there. We have received permission from the Russian Orthodox Church."
"Then here goes."
Immediately after Kanzaki said that…
Nanasen.
A flash of light was emitted from the space between the scabbard and the sword's hilt. Immediately afterwards, the scaffolding between Kanzaki and the metal balloon was sliced to pieces. The destruction stretched all the way to the metal balloon.
There were no sparks.
That quick slicing attack that used many wires sliced through everything before her like it was clay.
However, the massive amount of wreckage fell in a distinctive way.
It was different from being blown by a strong wind in a single direction.
The countless pieces of wreckage were blown in all directions, with the spot the metal balloon had been in at the center.
"It seems that it truly was filled with something like a gas. However, I do not know if that alone is providing the lift it—"
She trailed off because the scaffolding below her feet wobbled slightly.
It sank down about ten centimeters.
But Kanzaki sensed it as an instability like a suspension bridge having the wires supporting it snapped one by one.
"The destruction of the balloon has caused a change in Radiosonde Castle's altitude. We have been able to determine the specs of each individual balloon due to that. It seems that the gas in the tanks is indeed what is providing the lift. I will be sending you the procedure with which to remove the gas. The work itself is simple, but given the scale of the fortress, you cannot waste any time."
A few diagrams and values floated up in Kanzaki's mind. There were no major differences from what she had been guessing. The only real difference was that the time limit was rather harsh.
"So instead of just destroying them, I will be opening a hole in the balloons to remove the gas gradually?"
"If you destroy them too much in a flashy way and the rate of descent increases more than expected, we will have no way to fix the problem."
Kanzaki circled around, avoiding the scaffolding she had destroyed, as she ran along the lowest level. Radiosonde Castle was a few dozen kilometers long, but Kanzaki used her abilities as a Saint to run faster than the speed of sound.
"…Time for the first one," Kanzaki muttered when she arrived next to one of the giant metal balloons a few dozen meters across.
That one would be the test case to see if the theorized method would actually work. The situation could change greatly depending on whether she succeeded there.
"First, you need to greatly reinforce the side of the balloon. If you just opened up a hole now, the gas flowing out would force the hole wider."
"So it's like putting tape on a normal balloon and then stabbing a pin through it. It will also be perfect for installing a spiritual item that will act as a valve."
"The balloon's estimated strength is on the level of thirty millimeters of steel. We think that they were made intentionally fragile so that a ballistic missile would have immediately and catastrophically brought it down. You need to open a hole about thirteen millimeters across, but don't go through it all at once. Be careful and take at least a hundred seconds."
"Yes, the Japanese love our stories about water dripping down from a stalactite and wearing down the bedrock. We have plenty of spells to go along with that."
If one ignored the special examples like Saints such as Kanzaki, magic had nothing to do with talent and was in fact usually developed to be used by those with no talent. It seemed a lot of her predecessors had felt that magic was more suited to deliver slow and steady results piling up on each other rather than to bring out some great phenomenon all at once.
Kanzaki pressed a piece of paper against the side of the balloon, and it stuck there like a wet cloth. She then added many more. Before long, armor three meters square and five centimeters thick was covering the side of the balloon.
"…The Japanese really like those paper walls, don't they? They can stop blades and bullets."
"The idea is not all too rare. In places like China, armor was made of bundles of paper. Well, it was something like covering your entire body in phone books, so it was not very lightweight."
On top of that wall of paper, Kanzaki attached a device made of a few wooden sticks that were bound by cotton strings. It looked a bit like the compasses used by ancient scholars and a bit like tools used to dig wells.
"As this one is a test, I will watch it all the way through to the end, but there is nothing for me to do while it digs through it. There would normally be no reason for me to stick around and watch. Once I confirm that this one succeeds, I will leave the rest at this point and head for the next balloon. That will save a lot of time."
Just in case the balloon burst, she kept her distance and made sure she had a path to an ascending staircase planned. Kanzaki then sent magic power through the digging spiritual item and gave the signal.
An unpleasant sound like a pencil being sharpened reached Kanzaki's ears.
"For now, there does not seem to be any danger of the balloon wall bursting."
"The hole has been confirmed… The expected amount of gas is being released. Radiosonde Castle's rate of descent has increased, if only by a little."
"Contact me if you detect any problems. By expanding the stake used to dig, I can seal the open hole."
As she spoke, Kanzaki jumped from scaffolding to scaffolding.
As she had announced, she did not stay to watch each and every metal balloon as the hole was being made. She set up the spiritual items and then headed towards the next balloon.
"The effects from the interference to the seventieth balloon have been detected! Radiosonde Castle's altitude has fallen to eleven thousand meters!! The atmospheric pressure countermeasure spell is under quite a bit of stress!"
"Where is it currently!? Should we drop it into the Indian Ocean or the Pacific Ocean!?"
"Radiosonde Castle is currently passing over Korea. The Pacific is the only option now!!"
She had destroyed the first balloon when it had been near the center of Eurasia.
Radiosonde Castle's speed was much greater than Kanzaki had thought.
She hurried for the 71st balloon.
"Do you know where in the Pacific Ocean we are dropping it?"
"There is an area of ocean with a depth of six thousand meters located 1,700 kilometers north-northwest of America's Midway Atoll."
Kanzaki charted out the general route it would take from its current location to the next location.
(…It's going to pass over Japan.)
Her face gradually paled.
(The route cuts straight over Academy City!?)
"Agnese, it's an emergency!! Please calculate a method of interfering with Radiosonde Castle's balloons that will take a more circuitous route!!"
"Hah?"
"Passing over Japan may be fine, but passing over that city is bad!! If Radiosonde Castle was constructed in order to be dropped on something, the target is likely-!!"
Suddenly, a tremendous amount of static assaulted Kanzaki's ears. Immediately afterwards, the magical communications line created by the spiritual item was severed.
Someone had clearly magically jammed the magical signal.
(So they don't want me saying anything unnecessary, hm?)
Radiosonde Castle simply slamming its entire giant form into the ground was not the only threat. If it disassembled into smaller parts and had those parts rain down on the surface, it could create damage on a large scale. It could carry out a large-scale bombing of Academy City while the main body was allowed to safely land due to the efforts of Kanzaki and the others.
That was the logical thing to do.
However, if the people behind the fortress were the type to give their own ideas precedence over what was to come, it was still possible they would just drop Radiosonde Castle directly on Academy City without thinking about what that would mean.
Magicians were beings that would do that kind of thing.
Kanzaki and the rest of Necessarius existed to stop that from happening.
(But that jamming came with such pinpoint timing. I doubt that they would have been able to do that if they were simply collecting information remotely. That means… some portion of the enemy is onboard this fortress which is going to be sent crashing down…)
Kanzaki heard an odd sound, and she took a defensive stance.
It was a high-pitched noise like a crystal glass being hit. It did not repeat just five or ten times. Instead, it continued irregularly for quite some time.
The source of the noise was…
"Above!?"
The moment Kanzaki realized that and jumped back, something fell on the spot she had been standing in an instant before.
It was not a human.
It was a cylinder made of heavy stone with a diameter of 55 centimeters and a height of about a meter.
The drum-like object moved around like it had a will of its own, and it turned to face Kanzaki.