Shiori hesitated, then nodded. "We keep it between us."
Nonoka's smile deepened. "Some codes are only meant to be discovered by friends."
They had met three years ago in a cramped university study room and kept meeting ever since: not by schedule but by a gravity that pulled them together whenever one needed the others. Tonight, the gravity was a single string of numbers.
Shiori shrugged. "Or something left for us." Her voice carried the careful steadiness she reserved for when she wanted to be believed.
When they finally stood to leave, Sena slipped the novel back into her bag. She tapped the spine where the page had been marked and felt the echo of ink. "Tomorrow," she said. "We start with the library archives. At nine."
Nonoka closed her eyes for a moment. "Try breaking it in pairs," she suggested softly. "01–10–14–51–9." She opened one eye and met Shiori's. "Or think of it as coordinates, like latitude and longitude without the minus signs. Or a phone number missing a country code."
They stayed in the café until the lights dimmed, trading theories: a meeting time hidden in plain sight, a train platform number, a puzzle made to test whether they still remembered how to look for each other. Outside, rain traced silver lines on the windows. Inside, their conversation braided past and present—old friendships, small betrayals, a promise none of them had spoken aloud: to follow clues, even when following meant stepping into the unknown together.
"011014519," Shiori said aloud, testing the syllables like a key in a lock. Sena leaned forward. Nonoka's fingers tapped a rhythm on the table, matching a memory only she could hear.