Yuri is not only romance, this is quite an outdated view of yuri (reading that one interview with Iori Miyazawa, Otherside Picnic author, would clear up a lot of things about the modern understanding of the genre). Also shoujo ai is a crappy tag and should be removed from mangadex altogether like it thankfully was from vndb, a made-up term that causes more confusion than anything.
That said, yuri here is indeed subtle, but it's there if you look for it. The series wasn't so much axed as both the author and the editors didn't really know what to do with it, since it was not a typical Yuri Hime story (a bit too shounen-ish) and Shiroshi never thought it'd get serialized there in the first place so only had plans for a short manga.
Incidentally I can't help but recommend Shuumatsu Sekai Yuri Anthology where Shiroshi acted as a setting assistant/supervisor for most of the featured stories. Not sure whether it's already translated or not.