yes right, that's what I also thought
Well, I didn't see it like that. To me it was more like, the seme wasn't feeling that satisfied with the ways things were being with her ex gf, he wasn't sure what was it, so he thought that he wanted to try the other way around because it definetly felt better than he what he was feeling. He thought it was a position matter, when it was a partner matter actually. He doesn't feel the need to be in uke's position with Ten-san, since he feels satisfied the way things are. He feels satisfied enough to not think of changing.
Ten offered to penetrate him, but he was more focused in doing the other way around. Ten would do it for him, he was insecure, but he would do it. But Waka didn't have the need anymore because his partner, this time, was fulfilling.
It would have been great to have a reversible couple,but I like the story this way too. Since it became a matter of looking for what really makes you feel satisfied physically and emotionally
Mmmm I kinda wanted to see the seme bottom though... like, the whole story revolves around that point, and in the end its quickly dismissed like "oh yea, my previous relationship ended because I wanted to bottom, but now im gonna top!"
It also feels a little selfish from the uke, he wants to bottom so bad but can't fully grasp that seme wanted to know how it felt like too...
Still, I liked the story