Likely the most popular running route in all of Japan. Some races have been held, and likely there have been some very fast times. Note that runners must go counter-clockwise.
Here is a Strava segment: https://www.strava.com/segments/2446656 (Current CR's are 15:35/Male; 18:16/Female, out of 13,494 runs).
Since I hold the current Strava record, can I submit that to be recognised as the official FKT? ;-)
Yes you can. You could take a few minutes and research if faster times have been set in races?