4/5 premise.
2/5 delivery.
3/5 grammar.

RPC-421 initially began as an urban legend among shools in Central Asian and Eastern European regions.

This is really confusing. 421 isn't an event or an illness, it's a physical object. It makes no sense for it to "begin".

I kinda like the aesthetic/thematic aspect, but I feel it's been explored in a subpar direction. I feel it would've been far more enjoyable to discover the iron pot itself at the end of the article, with the primary anomaly being the voice in the school — this would've given the article a sense of progression, in that we are introduced with an innocuous aspect of the anomaly and the more gruesome aspects are later revealed.

Nevertheless, it makes for a nice read. I really liked the use of gray coloring in the audio log.

+3

thanks to venyson does not match any existing user name and TTPY for the crit.

although there's a minor spelling mistake:

No historical reference to RPC-521 was discovered except for one excerpt in a Kyrgyzstan storybook. Though, this connection is loose and can't be reliably verified.