

Numbers stations were prominently used during the Cold War. A boy was tuning the radio in the snow mountain and happened to tune the shortwave of codes. 1st year work 2016 by Ryotaro Miyajima, Tokyo University of the Arts, Graduate School of Film and New Media, Department of Animation. (Source: Geidai Animation)
No confirmed United States source. It's officially listed on the services below, but regional availability isn't confirmed — check the link.
These services list this title, but we couldn't confirm it streams in United States specifically. The link opens the official page.
Content similarity + the AniList recommendation graph