Natsuki Fujii tries to blend into her new high school. She loves art and hates drama. That should be simple, right? After the first bell rings, something about her homeroom stings. She can’t shake the feeling that people are meeting after hours—in the dark, by her desk. Does your school have that hidden layer too?
Natsuki sits by the window, drawing between lessons. Lisa, her desk neighbor, leans over. “Weird, isn’t it? All first-years get warnings about Room 3-B, but nobody talks.” They share glances, both pretending not to care, but the rumor sits in the back of Natsuki’s mind.
Haru, cheerful by nature, joins at lunch. “Don’t skip homeroom today,” he winks. “Today, those who vanish might be you.” He jokes, but his eyes dart to the closed doors, flinching at each bump and shout. Does he know more than he says? Why hold back?
Two days later, Natsuki stays late to clean up after Art Club. The halls are split with light bars from old bulbs overhead. She tiptoes to 3-B, keys rattling in her pocket. Inside, she catches Lisa, Haru, and two other classmates bending over a box of old letters by the back wall. 
Lisa starts, almost drops the box. “S-sorry. We thought you might not come.” Haru, calmer now, closes the door. There’s enough hush in his voice for all: “We meet here every month, when the moon’s out. There are secrets about this school, Natsuki. Things teachers don’t know.” Natsuki tries to laugh it off but stops when she sees each letter holds the same odd sign-off—three spirals inked in black. She doesn’t tell them about the note slipped under her door that morning.
Their work? Trying to tie these lost letters to students who have gone missing. Lisa thinks school authority is hiding something. Haru says, “Imagine finding where everyone who vanished is, what would you ask first?” Natsuki doesn’t pull out her hidden letter, but sets her mind to helping—for now.
“Meet again tomorrow,” Lisa says, hope flickering, “You aren’t scared, right?” Natsuki shakes her head. After curfew that night, another note comes under her door. Spiral, again. Someone knows she was in 3-B. She wakes in cold sweat, clutching the note, thinking, who is in her class, really?
Next: while helping, Natsuki finds a ripped ID badge, scorched at the name. Under the footstand, caked with mud, she sees distant initials and a shred of uniform fabric that isn’t from their school. She stares at Lisa: “We need to find out where this badge came from.” Lisa agrees, but tugs Natsuki aside. “Stay low, okay? They’re watching us.” A clock chimes. In the near dusk, footsteps stop behind the door. The arc closes as someone turns the handle. 
