With all the content from Splatoon 2 and the Octo Expansion exhausted, the Splatoon manga adaptation gets into some original plots – presumably before it steps into adapting Splatoon 3 content. As such, Team Blue finds themselves up against yet another fearsome foe: themselves.
This volume contains chapters fifty-eight through to sixty-one.

Front cover of the fifteenth volume of the Splatoon manga, featuring Shadow Goggles and Goggles
Team Blue engages in their most complicated Turf War yet as they combat the Shadows, whose personalities are mirror reflections of Team Blue’s own! The result of the challenge will determine the fate of Inkopolis Square!
I’d guess that the chapters in this volume were produced pre-Splatoon 3. Seems like we’ll have to wait a bit longer before we get to see the likes of Deep Cut or any of the third game’s story content adapted into the manga. What does Sankichi Hinodeya give us to fill that gap? Mirror matches, effectively.
Of course, a new foe appearing means that some of Team Blue’s stronger opponents team up to take them on. Seems that their role is only to show how powerful these Shadows are supposed to be, perhaps an attempt to bring in some kind of stakes for these generally low-risk Turf Wars.
Whilst the shadows are pretty much the polar opposites of their original selves, there is still plenty of time for goofiness. In fact, we get double the goof, as we have two versions of Goggles running around. Seems there’s at least one aspect that Goggles and Shadow Goggles have in common. Unfortunately that does mean the return of that one lame running gag, but this time doubled.
It’s a little odd getting used to playing Splatoon 3 with its new lineup of special weapons, and going back to this manga to see the Inklings are still using those from Splatoon 2. It definitely ages things a bit here. Oh well. Still get a fairly decent Turf Wars match out of it, for the most part. As far as the Splatoon manga adaptation goes, it’s fine.