I've located the orginal post about it on the forum
https://sonotaco.jp/forum/viewtopic.php?t=1723&highlight=20080428
I am working with the Google Japanese to English translation
External Quote:
I received some inquiries about this capture.
Therefore I note the information of this capture in the image, and appeal my understanding.
Though the movement is rather tricky, now we are thinking the most probable explanation of this event is a pair of birds.
Because...
1. Many birds or bats that are lighted by ground lights have been captured by this camera.
2. Some movement like faction can be seen on the last part of the video.
3. The imaged curvature is very large against its angular velocity.
4. There are no simultaneous observation reported though this area is observed by several stations.
5. 3. 4. means that this event happens within the distance of a few hundred meters.
There is a lot of speculation about what it might be Birds, planes etc are suggested and it seems there was interest at the time in the video.
There is reference to a higher quality video that was shared at some point, but has since been removed, this may be the source video posted on X but I have also attached the original video from the fourm.
More data is presented in a overlay image
View attachment 82619
Tokyo1_S2
139d38m E, 35d39m N in Setagaya-ku, Tokyo
https://maps.app.goo.gl/dVSPjRMA2v9S9kNE7