Remember when Aoki had that sleepy long cellphone call with Rin? And he said he wanted to show her the sea? There is a landscape early in this chapter that shows the sea, lets us know we are near Aoki's home town. It took me a while to realize that Houin had gone along, I think Watashiya has a generic "pretty blonde" so that Rin, her mother Aki, and Houin all can look rather alike.
In a way the tampon scene -- I think Watashiya thinks kids are reading this and wants to do a little "sex education" just as the teachers are discussing, to make it all clear and normal so the boys won't get all freaked out about menstruation etc. I don't know, it's also possible that it's just another excuse for fan service. But that is not the feeling I get from this, it doesn't strike me as cheesy.
And let's see, when Rin gets into bed with Daisuke -- Watashiya is trying to show how she is growing, her bones are getting long and she's getting taller, but it makes her look so gaunt and thin. In a way she looks more like a child now, stretched out and flat, than she did when she was smaller and rounder.
I am curious about what Daisuke's sister is saying throughout this chapter. I can't make much of it out but when she first meets Houin she calls her "Bouin" which makes it obvious that Daisuke has used that nickname.
Perhaps what happened with Daisuke was similar to what happened a while ago with Reiji...
http://www.mangafox.com/manga/kodomo...03/c019/6.html