Chapter 70: The Cold-Blooded Arithmetic User Arc

"Honestly… why does it have to be in such a remote place?"

A student walks along, brushing away the snow each time it settles and turns the crown of her deep-indigo twin tails white. This is Hayase Yuuka, the treasurer of Seminar—the student council of Millennium Science School—and also the de facto stand-in for the missing council president, who vanished months ago after taking responsibility for an incident she caused. Seeing Yuuka busily making the rounds of clubs across Millennium on official business is nothing unusual, and today is no exception.

"Just because I had time before the next bus… coming on foot was a mistake, apparently."

She had taken the monorail from central Millennium to the outer district and planned to go the rest of the way by bus—but by sheer bad luck, the next one would not arrive for another twenty minutes. Factoring in the possibility of traffic delays, she calculated that walking would probably be faster.

"Still… the Shipbuilding Engineering Department, huh."

Yes—her destination today is the Shipbuilding Engineering Department, one of the largest clubs in Millennium. During the recent crisis in Kivotos, she had heard that, thanks to instructions from their department head, Seira, the damage had been kept to a minimum. Even so, many details still needed verification. On top of that, she wanted to check how preparations were progressing for the upcoming Millennium Prize.

"Well, I’m sure it’ll be fine."

The Shipbuilding Engineering Department is a long-established club that has consistently produced solid results. Its activities tend to stand out more outside the school than within it, but it has never caused any serious problems.

"I’m here… and wow, it’s as impressive as ever."

Yuuka looks up at the red-brick warehouse before her. She has visited several times before, and unlike the futuristic high-rise buildings that crowd central Millennium, this structure’s old-fashioned atmosphere is something she doesn’t dislike.

"Please stop."

"Hm…?"

As she tries to enter the Shipbuilding Engineering Department’s grounds, a holographic image of a girl suddenly appears before her. Slightly smaller than Yuuka, with short blond bobbed hair, the girl’s outfit is clearly not a Millennium uniform: a jacket worn over a high-cut leotard, with several mechanical floating devices hovering around her. It is, to say the least, an unusual appearance.

"Was there someone like this…?"

While not quite on the level of her friend Ushio Noa, Yuuka prides herself on her memory. She remembers the faces of most Millennium students, yet this girl is not among them. Perhaps, like Alice from the Game Development Department, she was someone the Shipbuilding Engineering Department had brought in from elsewhere? As Yuuka turns this over in her mind, a figure emerges from the building’s door.

"Department Head, an intruder has been detected. How should we proceed?"

"Ah—she’s not an intruder, she’s a guest."

Standing about a head taller than Yuuka is Karaho Seira, the head of the Shipbuilding Engineering Department. She reassures the holographic girl that Yuuka is not an intruder. Hearing this, the girl turns back toward Yuuka.

"I see. My apologies. I am the missile cruiser 'Martinique.'"

"Um… Department Head Seira. What exactly is this…?"

The girl has introduced herself as a ship, but she certainly doesn’t look like one. At least to Yuuka, she appears to be nothing more than a girl in a rather revealing outfit.

"I’ll explain that too—let’s head inside first."

As Seira turns back toward the building, the hologram flickers out. With little choice, Yuuka follows after her.

Inside the office, the same girl is waiting for them, as if she had taken a shortcut.

"Alright, let’s go through this step by step."

"Yes, please."

The two sit down on the reception sofa, and the conversation begins at once.

"You’ve heard that the piece we’re submitting to the Millennium Prize is a missile cruiser, right, Yuuka-chan?"

"Yes, I have."

Recently, Kivotos had been covered by a red sky and attacked by the Forces of Color. During that incident, many enemies appeared in the Millennium district as well. While defending alongside other students, Seira had carried out support attacks using a newly completed missile cruiser—something Yuuka had heard about through rumors and official reports.

"That missile cruiser is Martinique-chan here, and… we’ve packed her with all sorts of new mechanisms."

"I see…"

Seira then gives a concise explanation of Martinique, describing how they made extensive use of data obtained through cooperation with other clubs, while still keeping development entirely within the Shipbuilding Engineering Department.

"And… missiles and the integrated air-defense system are important, sure, but this right here is what we put the most effort into with Martinique-chan."

"NEREIS…?"

Yuuka reads aloud the title on the informational material Seira hands her.

"Responsive Naval Equipment Expansion Interface—Naval Equipment Responder, Enhanced Interface Systems, abbreviated as NEREIS. It’s a naval combat-support AI developed by the Shipbuilding Engineering Department, designed to embed a ship-specific integrated personality AI. Through a dedicated controller terminal, it can handle combat support, situation reporting, and autonomous actions under broad command instructions."

"So, in other words, that girl over there is a holographic projection of the AI personality set for the cruiser Martinique?"

"Yeah, that’s right. It would be pretty dull if it just showed messages on a terminal, so we developed this system instead."

Seira beckons Martinique closer and pats her on the head. There shouldn’t be a physical body—after all, it’s only a projection—but Seira moves her hand as if an actual girl were there, and Martinique responds in real time, as though she can truly feel it.

"Now then—today you came to check on our progress for the Millennium Prize, right? Everything in order?"

"Yes. From what we’ve seen, the Shipbuilding Engineering Department doesn’t raise any concerns. Everything seems fine."

Many clubs in Millennium have quirks or are anything but straightforward. Even the Engineering Club, consistently one of the top performers, has its share of eccentricities.

Perhaps because the Shipbuilding Engineering Department works on long-term projects like warships, they maintain a practical and grounded approach. Simply put, there aren’t many problem students for a club of this size.

"Also… could you tell me about the damage the Shipbuilding Engineering Department suffered during the recent incident? I’ve heard the members worked hard to keep losses minimal."

"Oh, yeah, that was quite something. These weird robot-like things suddenly swarmed all over…"

After confirming the department’s recent status, Yuuka prepares to return to central Millennium—when suddenly:

"Seira, I’m here… Yuuka?"

"Se-Sensei!?"

"Oh, Sensei’s here."

It’s the advisor of the Federal Investigation Department, known as Schale. Yuuka has known him since he took up the post and has met him many times before—but she’s still surprised to see him here.

"W-why are you here…?"

"I never really had the chance to properly visit the Shipbuilding Engineering Department. I also just returned briefly from the Hyakkiyako operation, and thought I’d spend today somewhere peaceful."

Sensei has visited the Shipbuilding Engineering Department twice before: once during a brief tour of Millennium, and once while pursuing Kurosaki Koyuki, who had taken refuge on a ship at Odysseia Maritime High. Both visits were under high-pressure circumstances, leaving little opportunity to interact with Seira or the department members. Today, however, he came specifically with time to spare.

"How’s Yuuka? Working?"

"Yes… I’m on official Seminar business. Haa, why is it that whenever Sensei sees me, it’s always when I’m not at my cutest…"

"I think it’s wonderful that you’re working so hard, Yuuka."

Hearing those words, Yuuka’s cheeks—and even her ears—flush crimson. She turns her face away, trying to hide it.

"A-anyway! My business at the Shipbuilding Engineering Department is done, so I’ll be heading back!"

As she steps outside, both Seira and Sensei suggest, "Since you’re here, why don’t we take a look around together?"

Yuuka, unable to refuse when kindness is offered, ends up accompanying the two—bonding with them over their shared enthusiasm for the romance of naval engineering.