Reki, a high school sophomore and skater, is addicted to “S,” a highly secret and dangerous downhill skateboarding race that takes place in an abandoned mine. The skaters are especially wild about the “beefs,” or heated battles that erupt in the races. 
 
Reki takes Langa, a transfer student returning to Japan after studying abroad, to the mine where the races are held. Langa, who has no skateboarding experience, finds himself pulled into the world of “S”... 
 
(Source: Aniplex of America)
 
Note: On March 13, 2021 a recap episode (9.5) went on air, postponing the broadcast of the regular episodes by one week.