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Assured Destruction

Summary:

The day after the Yachiyo Cup concert, Yachiyo receives an unpleasant yet enlightening visit.

Written for Cosmic Princess Kaguya! Week 2026 Day 3 (prompt: “Avatar/Self”).

Notes:

Thank you to Lace for beta reading.

(See the end of the work for more notes.)

Work Text:

“I lost all my progress on my homework assignment because of that stupid moon virus crashing my laptop. Yachiyo’s stunts seriously went too far this time.”

“bro even the police are saying it wasn’t a stunt. yachiyo haters have got to get a grip. also this is why you save your work lmao”

“Tsukuyomi bugged out and kicked me right at the end of the concert. Did my avatar get zombified into one of those lantern-head things? Everything seems normal when I log in now…”

“i saw a lantern head in AR with my smart contacts walking through tachikawa station. it stopped for a few seconds to bow to me. super weird”

“Maybe it was some jilted Kaguya fans taking their Iro P ass-whoopings way too hard, lol”

“With that kind of hacking capability? If that’s it, some otaku Mythos 9 dev is going on the industry blacklist for sure.”

As Yachiyo surveyed the social-media aftermath of the brief Lunarian invasion last night – standing a couple meters in front of the tall screen in her palace’s balcony room, its glow mingling with the soft orange-tinted light of the floor lamps – she found herself getting angrier with her people than she’d spared the energy for in a long time. She’d expected them to show up at the Yachiyo Cup concert from having lived it once already, of course, and she’d prepared herself emotionally as best she could for what it’d mean for her past self and Iroha – but the trouble the Lunarians had caused for all of these people besides the two of them hadn’t stuck much in her memory the first time around. Locking up countless device displays behind the face of their homeworld, darkening Tsukuyomi’s skies with swirling virtual clouds, hijacking humans’ avatars instead of summoning their own like in the battle to come… Even back on the moon, the intentions behind the higher-ups’ orders had often been frustratingly inscrutable, but –

“Were they trying to freak the humans out as much as they could, or what?” said FUSHI derisively from his perch on Yachiyo’s shoulder.

Yachiyo gave a defeated shrug. “Could be, for all I can tell.” After eight thousand years of companionship, FUSHI had an uncanny knack for giving voice to her thoughts sometimes. “If I’d realized how big a deal this was going to be, I don’t know if I’d have tried to play it off as part of the show. At least it looks like most people aren’t blaming me for the real-world stuff.”

“Well, I’m sure they trust by now that not even you’d go that far,” FUSHI said.

Yachiyo narrowed her eyes, though mostly teasingly. “What do you mean ‘not even’ me?”

“I’m just saying,” FUSHI began with a tiny playful bounce, “if you leave out the real-world disruption and the avatar hijacking, throwing people for a loop like that is right up your – ”

Just then, a ringing, crackling noise sounded from behind Yachiyo and FUSHI, at the opposite end of the balcony room – sending through Yachiyo the closest thing she could feel in Tsukuyomi to a chill. Whipping around to face the noise and seeing the shimmering cloud of firefly-like lights producing it, Yachiyo hurriedly brought up the Tsukuyomi access debugging log – and sure enough, the backdoor the Lunarians seemed to have found and used last night was being exploited once again.

What do they want with me? Yachiyo wondered distressedly, hearing FUSHI growl as the cloud of lights coalesced into a two-meter-high, yellow-tinted image of the moon’s near side. And are they here for Yachiyo Runami the human-made AI, or for the Lunarian I really am? I – I remember Yachiyo produced my graduation concert, so one way or another, I’m not about to get taken back again – right?

The image of the moon began to swirl, shifting into a ring-shaped portal of sorts – and through it stepped just a single one of the dull, interchangeable Ryousan-type Lunarians, the ones that the humans had taken to calling “lantern-heads.”

So not a force for fighting or capturing, Yachiyo thought with at least partial relief as she watched the portal close behind the Ryousan-type. Just a messenger.

The messenger began walking unhurriedly but steadily toward Yachiyo, not saying a word – maybe intending to try a contact-based data transfer. After the one its kin had forced on her eight thousand years ago, though – the one she’d had to vicariously re-live last night – she wasn’t taking any chances with another. She raised an arm with fingers splayed, and the messenger collided with a wall of invisible force, staggering briefly and stopping in its tracks once it regained its footing.

I have to admit, Yachiyo thought, being able to do this feels pretty good. Almost as good as swatting these guys away last night, when I realized Iroha wasn’t about to get us out of that bind on her own.

“Who are you? What do you want?” she demanded of the messenger. In this context, that should be non-Lunarian for “audio only.”

Sure enough, the messenger then spoke in a dry monotone, multicolored waveforms flickering inside its half-translucent head. “RELAYING MESSAGE: FURTHER ATTEMPTS TO INTERFERE WITH THE EXTRADITION OF KUUKAI-TYPE INSTANCE-ABAFBBA4A4C7F3 WILL RESULT IN YOUR OWN EXTRADITION. SIGNED: ROKUJINZUU-TYPE INSTANCE-DEA0.”

If Yachiyo still had a gut, it would’ve twisted up in unease. So that’s how it is.

“Message acknowledged,” she said, a bit more weakly than she would’ve liked.

The messenger gave a bow, and then vanished in a burst of smoke – leaving Yachiyo and FUSHI to sit in disquieted silence.

“Y’know,” FUSHI said, “I was mostly joking about the ‘trying to freak people out’ thing, but… that probably is why, isn’t it?”

“Huh?” Yachiyo said, the connection not quite clicking for her.

“I mean, like, with this threat just now…” FUSHI said. “If they’re bothering, they must think there really are things you could do to interfere, even on the full moon when they’re at maximum strength and taking it all seriously. And if they aren’t doing more than threatening you already, they must think it’d be more trouble than it’s worth unless you keep getting in their way.”

“…Maybe,” Yachiyo said, hesitant to share FUSHI’s confidence. “So you think the extra havoc they caused last night was meant as a threat too? But a threat for who?”

“Well…” FUSHI began, looking like he was still figuring out how to put it into words. “The Lunarians aren’t exactly impatient, right? So if Yachiyo’s powerful enough to be a thorn in your side, why go after Kaguya during a concert when Yachiyo’s right there, unless…”

“…Unless you want to capitalize on there being hundreds of thousands of humans watching live,” Yachiyo finished – understanding the argument now, at least. “And the device displays in the real world, and the Ryousan-types wandering around in AR – you think they weren’t just trying to get to me through the humans. They were trying to – to come off to the humans as something scary and incomprehensible. Something you shouldn’t mess with, no matter how big a fan you are of Kaguya – or of Yachiyo. No matter how much you’d hate it if they were taken away.”

“You probably put it better than I would’ve,” FUSHI said. “What’s that saying again? ‘The more scared a dog is, the louder it barks’? As a former dog, that does hit pretty close to home.”

“I mean, I think that’s losing the metaphor a bit,” Yachiyo said. “But…” She folded her arms in thought. How much do the Lunarians really have to fear from the humans to begin with?

Well… I can’t imagine it’s much. But maybe it’s not nothing.

Even before she first visited the Earth, Yachiyo knew enough about humans to know they’d been improving their technology over time. But after the eight thousand years of human history she’d witnessed, she understood it wasn’t just that – the rate at which their technology improved had itself been increasing. For an especially relevant example, over the course of just a couple decades in the past century, she’d watched them figure out how to build rockets powerful enough to physically reach the moon – and bombs powerful enough to cause devastating global quakes on the tiny celestial body. The Lunarians could deploy pre-emptive cyberattacks and other formidable countermeasures for a strike like that, of course – Yachiyo didn’t doubt that as of yet, they had a lot less to fear from the humans than vice versa – but maybe they still wanted to be cautious over the chance, however small, of a ruinous blow slipping through and connecting.

Yachiyo could shake hands with them on that, at least. The absolute last thing she wanted to see was a war between her new home and her old one, for both their sakes. And she knew that, despite her power and influence and the leverage they seemed to provide, a serious fight between her and the collective of her fellow Lunarians could never end in victory for her or those she sought to protect – only a messier, costlier loss.

So this is why Yachiyo didn’t fight for me alongside Iroha and the others at my graduation concert, Yachiyo thought resignedly. She knew struggling would only hurt her – just like me.


A few nights later, Yachiyo stood on a Tsukuyomi skyscraper’s rooftop balcony with FUSHI again sitting on her shoulder, the two of them summoned here alongside Roka, Mami, and Black OnyX so Iroha could tell them all the true story of Kaguya’s origins and impending fate. And once everyone seemed to believe it…

“Yachiyo, is there anything you can do to protect Kaguya?” Iroha asked worriedly.

I’m so sorry, Iroha, was Yachiyo’s answer in her heart. I’m just not strong enough. That’s why the river of time takes the course it does. That’s why the dream we shared wasn’t meant to be.

But Yachiyo’s role in Iroha’s life was to support her at a remove, unless and until she came to suspect the bittersweet truth – and so the answer that emerged from Yachiyo’s mouth was a lie.

“I investigated, but I couldn’t figure out where they’re accessing Tsukuyomi from. Sorry.”

“No, it’s fine,” was Iroha’s gentle reply.

I guess so, Yachiyo told herself. This won’t be a happy ending for us – but someday, it can still be one for you. And it’s a fine ending for me.

Notes:

The term “Ryousan-type” (リョウサン型) for the lantern-headed Lunarians comes from the official guidebook. The names given for the other types of Lunarians seen in the graduation concert battle are テンニョ Tennyo, ホテイ Hotei, コンゴウ Kongou, ボサツ Bosatsu, and ズイジュウ Zuijuu.