The Tag description is... Description: One character engages in a sexual activity by themselves. The use of objects as stimulus is acceptable (e.g. magazines, sex toys, exhibitionism). Other characters may be present, but no physical or mental interaction may occur.
I think that describes this pretty well, nowhere in that description does it say that the entire work must be only solo action, and the presence rule seems to cover this. There's a clear scene change (Akiguma is even in a different outfit)
Finally, for a practical standpoint, anyone who is looking for Solo action will be happy with at least the 1st half of this.
As Always, check the discord and join in on the contest where you can win a commissioned work of your choice. https://discord.gg/7w4vywM95P
14: eight => (counting) / eighth 23: not evening tightening => not even tightening 25: You can't => (a plea rather?) / Don't 25: gravity => (usually no need to be technical here) / your weight