This is sort of a flashback, although it doesn't really affect the plot. It starts out as a surprisingly close parallel to the banned episode 12 of Ultraseven, but it's clearly Asari's take on it. This is unusually serious, with some good-looking action.
As I've mentioned before, I'm using two sources for this. One is the raws that I'm editing, which are cleaned scans of the Kodansha 11 volume compilation, and the other is uncleaned, (slightly) higher resolution scans of the 13 volume (but less complete) Tokuma Shoten compilation. The Kodansha version does not include chapter numbers, but in the Tokuma Shoten version, this is listed as chapter 12 (despite coming right after chapter 26).
This chapter closes out volume 3 of the Tokuma Shoten compilation, however, and starting with volume 4 the chapter numbers are dropped entirely. So it's not quite clear whether the next chapter is supposed to be 27 or 28. I'm going to number this chapter as 27 and the next as 28 so that file sorting works as expected.