Chapter 20:
Ch.2 – EP20 Sandra Appears: A Difference in Class
Caïssa’s Child: The Boy Who Beat the AI
Around A-01, it felt as if the air conditioning had kicked up a notch and the temperature dropped.
But that wasn’t it. She had only walked in.
Long blonde hair, blue eyes, white skin. A sleeveless white one-piece; gold-thread hair swaying below the knees. A girl like a shard of cold Eastern European glass—Sandra.
Staff from a Frostfish-affiliated sponsor exchanged a few words with her and gave short nods. Black patches with a white crown. On the corners of their folders, a small Engine Lab logo shimmered.
Facing her was Yūto. Eighteen, representing Aichi. A regular at nationals, this time he’d also edged out a local powerhouse with ELO 2000 and had plenty of momentum.
(Even if she’s ELO 2400 there ought to be gaps. Hang on and land a giant-killing—)
Reporters included, spectators layered two and then three rows deep behind the standers.
“YOROSHIKU ONEGAISHIMASU.”
Sandra smiled in broken Japanese and offered her right hand. A handshake.
(Wow, she’s really cute.)
Something warm bloomed in Yuto’s chest for an instant.
But—when White’s fingers reached for the first piece, in that slight motion, a cold pressure ran through.
(What is this… why did I just think “cute”? This fierceness… I’m getting swallowed.)
The audience buzz sank lower. Beside the board, a digital display showed both players’ time controls and an AI-driven evaluation bar pulsing like breath.
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【The Start (White: Sandra, Black: Yūto)】1. e4
Sandra’s white pawn moved forward gently yet without hesitation.
Yūto replied at once.
…Nf6 (Alekhine’s Defense, good, inside my prep.)
2. e5 Nd5
Yūto (Here we go, forward. She’s claiming central space. The knight drops back to d5.)
3. Nf3 d6
Yūto (This is where it matters. The balance between White’s central pressure and Black’s counterplay.)
4. Bc4 Nb6
White’s bishop to c4. A knife-like diagonal. Black’s knight to b6 to step out of that line.
5. Bxf7+ Kxf7
Spectator: “Huh, an immediate check!?”
White’s bishop smashes f7. Black’s king Kxf7 swallows it and stands exposed. A murmur runs through the hall.
6. Ng5+ Kg8
Yūto: “Another check!? —Stay calm, just step the king back.”
Black’s king goes to g8. The eval bar dips to Black better.
Yūto (−2.8. Fine, not bad. I can even see the win.)
Sandra’s expression doesn’t change. Her eyes, as if tracing an engine log, let the shadows of the pieces slide.
7. Qf3 Qe8
White queen forward. Black instantly sets a net of defense with Qe8.
Yūto (Yeah yeah, aggressive, aren’t we. But the firmer I defend here, the better it is for Black.)
8. e6 h6
White’s e-pawn drives in deep alone.
Yūto (−3.0. Eval tips further to Black. Black better. Time to accelerate—)
Black plays h6—shooing away the Ng5 idea and taking a breath.
9. Qf7+ Qxf7
Beside the board, the evaluation bar paused for a split second—
Then jumped from −3.0 to +99.9 (≈ forced mate).
A few spectators clapped hands over mouths and double-took at the board.
(H-huh? What just happened? Black defended, and yet—)
The meaning of that numerical violence didn’t cohere for Yūto.
(…Qxf7 should be correct. Trade off White’s queen, then surround the isolated pawn on e6—)
Sandra didn’t so much as twitch a brow.
Her blue eyes, like an AI touching the right answer, subtly raised in luminance.
10. exf7#
White’s e-pawn moved forward, consuming Black’s queen on f7 as it went.
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…Kxf7 is restrained by White’s knight on g5. h7 is also forbidden by that knight; g7 is blocked by a friendly piece; f8 is sealed by Qe8—there is nowhere to run.
On move 10, in just five minutes—a pawn mate.
The piece-landing sound was like a small bell. At the final strike, the air over the board froze transparent.
The black king on g8 has no escape.
g7 has been blocked since the opening bishop, h7 was self-removed by h6, f8 can’t be stepped onto because of Qe8.
And the shadow of White’s pawn that arrived on f7 gently, yet perfectly, stole the king’s breath.
The eval bar stopped at +∞, and around A-01 a delayed murmur rolled in.
“Mate in 10…?” “A pawn mate, it’s like magic…” “In the Alekhine, this is a thing…?” “So this is what ‘a different class’ means—”
Yūto sat stupefied in his chair.
(A pawn goes forward? The king can’t move? No way. My run at nationals ends with this…?)
Sandra lowered her eyes to the clock and relaxed the corner of her mouth by one millimeter.
—As if an AI that named the correct answer was saving its log.
“ARIGATO GOZAIMASHITA.”
She thanked him in broken Japanese and pushed back her chair. Even that motion had no waste.
In Yūto’s ears, only the far-off sound of the air conditioning remained.
(What happened? Where—)
A staffer impassively collected the scoresheets, and at the edge the Engine Lab logo flashed once more.
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【Visualizing “Class”】<PGN>1. e4 Nf6 2. e5 Nd5 3. Nf3 d6 4. Bc4 Nb6 5. Bxf7+ Kxf7 6. Ng5+ Kg8 7. Qf3 Qe8 8. e6 h6 9. Qf7+ Qxf7 10. exf7#</PGN>
※ If you’re new to chess and want to follow the moves,you can try copying the PGN between <PGN> and </PGN> into the analysis board on Lichess(https://lichess.org/analysis).
Please note that, due to site limitations, copying the text may take a bit of extra effort.
The final position is beautiful.
White’s pawn on f7 sits where a crown would be; e8 is the hole left by Black’s vanished queen.
h6 invited self-collapse; Qe8 stitched shut the king’s escape with his own hand; Qxf7 drew in the last needle.
Those three small choices decided fate in five minutes.
Off the board, layered whispers.
“The opening principle ‘early queen trades are safe’—this is an exception.” “e6 was poison.” “9…Qxf7 is the fatal wound. 10.exf7# is an engine move.”
“In the end, ‘class’ is whether you can notice the exceptions.”
“The speed of feeling is different.”
The light over A-01 seemed to ease back a notch. With eyes still on her back, Sandra cut through the crowd and walked.
There was no sound of ice melting. Only the silence of those who now understood ice’s shape remained.
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【Yūto’s Long Minute】(Instead of Qxf7, what about Kh7? No, without 7…Qe8 there’d be an escape route to f8—
Did h6 complete the mating picture? Then if I remove 8…h6—
No, 8…c6? …dxe5? …c5?)
As the clock’s hand marked one minute, Yūto ran through dozens of what-ifs.
But that quiet tenth step poured water through every circuit in an instant.
(“Class” is—this.)
He finally exhaled. Not deep, a small sigh.
Then he looked at the curve of his own signature marking the loss—with a little frustration and a little respect.
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Down the aisle, the white dress slipped around a corner.
Sandra tossed an empty plastic bottle into a trash can with precision and lifted her gaze just a touch.
Her sponsors paced alongside, handing over bundles of data.
The Engine Lab logo. The Frostfish crest.
And from somewhere in the venue, soft applause rose toward her back.
Applause born purely of admiration for the beauty of a “mate in ten.”
Sandra didn’t look back. AI doesn’t look back.
She simply walked toward the next correct answer.
(—The difference in class is the speed of the correct answer.)
Board A-01 was reset to its initial layout, new pieces set in place.
But on the retinas of those present, the moment White’s e-pawn crowned on f7, that small bell kept ringing for a while.
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【The Audience’s Margin Notes】“I’ve never seen a pawn mate in ten moves.”
“So this is how ELO 2400 moves…”
“I said she’s cute—I took it back in five seconds.”
“No, she is cute. It’s just—cute ice.”
“The difference in class literally turns into wind. The moment she arrived, it was cold.”
Laughter and sighs blended together.
A crowd on the verge of tumbling like dominoes finally, quietly dispersed.
Somewhere, a timer went beep.
The venue began another story.
But the story of A-01 had been perfectly closed in five minutes.
—A difference in class.
No explanation was needed anymore.
10.exf7#—that alone was enough.
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