Looks like this is the dragon girl from chapter 1 page 35. Which means the fish girl on that page is likely also coming in the future.
Question is, who is this dragon girl to Washio? I don't remember lizards in the monster class.
As usual we won't actually know until the tankoubon is released and we see the extended scene. This is NOT the first time they end up naked together, though, and it really might just end up being "cuddling naked". Indeed, I suspect it to the more likely outcome given the fact that it would be...
This paragraph shows you really don't get it. The first volume was not the sole "main story". Yami is not a side character. You need to let go of the idea that Hikari is the main character. She is one of them. There are more. We might even switch perspectives in volume 3 to Yuu
No, it's not. An analepsis is an interjected scene taking place in the past from the active narrative. The reason people like you are complaining about how long it is taking is specifically because it is not. You are still seeing Hikari's POV as the main plot. We know now that it isn't.