Yeah, way back when Shadow saved the Oriana kingdom, he (and Beta) got sucked to Japan. But, Beta dragged Akane back to Shadow’s world when they returned (mainly so that she can share knowledge of technology and stuff). So, this is probably shortly after Shadow returned in the story. In the LNs, that is pretty much the last we see of Akane. This feels kind of too important to just be manga filler, so I wouldn’t be surprised if the author was involved in this. Next LN volume is slated for release in April.