Only objects emit frequency, not living beings. Plants also emit frequency, but not plants that have consciousness. Therefore, no one can tune into Flain's frequency because he doesn't have one at all.
Most of the objects Flain is supposed to tune into have a more distinct and stronger frequency than others, which is why it didn't occur to him right away.
The wall has the exact same frequency as, for example, a speck of dust — nothing special. Flain had a feeling he had figured it out, even though of course he could be wrong, and that nothing could be learned from the frequency the wall emitted.
Flain quickly completed the 6th floor and found himself again in front of the wall.
"Hey Flain." Denji's voice called out again from the wall.
Flain focused and tried with all his strength to tune into the frequency coming from the wall — it sounded easier than it was to actually do.
