The next morning, Yoon-seo stands between seats 4A and 4B before anyone else arrives, waiting like a question that refuses to sit.

Do-hyun arrives to find Yoon-seo waiting beside his desk. Other students are still outside, leaving the confrontation bare.

They move to the stairwell between floors, where the concrete walls amplify every quiet sentence.

A close stairwell panel holds Do-hyun's face and the name he has avoided saying.

Yoon-seo hears her sister's name in a place where she did not expect it to survive.

The stairwell window throws a pale rectangle of light between them as Do-hyun says what the family never heard.

The stairwell falls away visually, leaving only Yoon-seo and the fact that grief did not give her ownership of the dead.

Do-hyun answers before kindness can catch up, and the sentence lands between them like a dropped blade.

Do-hyun decides that denial is uglier than proof. He unlocks his phone and opens an old photo.

The phone photo shows Do-hyun and Yoon-ah in school uniforms at a riverside railing. Yoon-ah's face is fully visible to camera within the photo, her blue ribbon and mole clear.

Back in homeroom, the ordinary seating chart becomes a map of hidden lives.