Um, the girl in the bottom (in the public bath tub) is Charlotte. At this time, her identity as a girl was known only to Ichika - who, after hearing her story, aggreed to keep her secret - and she had to act as a boy to the rest of people in school.
Since they are allowed to use the public bath in a very limited occasions, not entering the place might buy suspision from others. So she entered the bath - initially saying that she would stay in the locker room while Ichika was taking bath (Ichika loves the large public bath, BTW) but she eventually enters the bath and have a talk with Ichika.



I think I misused the term 'openness' while describing Rin's character.
Because they(Rin and Ichika) are childhood buddies, there are moments when they view themselves not as a possible couple, but just old friends.

I believe Rin's 'openness' is only apparant when wearing a swimsuit, since she is the only one who aggressively attempts physical contact with Ichika
(That's when she treats him as a childhood buddy, not a love interest - rather, momentarily forgetting about having a crush on him - so it is not a physical contact as in a romance, but rather like fooling around (mock strangling or riding on his shoulder... something like that))

Normally, Ichika would blush and would not know what to do when suddenly hugged by a girl, but Rin seems to be an exception (even in her swimsuit) mainly because of her lack of glamour...
(He strictly keep this impression to himself - or tries not to think about it at all - since Rin would go berserk if she hears this from him or even catch him thinking about it (especially about the boobs))

However, when she views him as a love interest - quite easy to distinguish because she would shows the sign of shyness and strong 'Tsun' while conversing with Ichika in this manner - the change in her manner would cause him to view her as a girl, sometimes making him blush.

It could be a little confusing because Rin is every bit as shy as other girls (maybe except for Laura who doesn't seem to understand the embarrassing aspects of romance) when it comes to the aspects of romance. It's just that there are moments when she doesn't(forget?) see him as a love interest.

The other girls, however, mostly see him as a love interest - except when they get mad at him and treat him like a punching bag - so they would hesitate to initiate even the modest form of physical contact out of embarrassment - such as holding his hand or taking his arm which they accept as an external signs of romance between a couple.
(It might be just an act of friendliness to casually hug or receive a hug from friends (of opposite sex) in American culture, but apparantly that's not the case in this part of the world - although people here (especially young ones) seem to become more and more open to those trends nowadays.)

Remember the 'maybe except for Laura who doesn't seem to understand the embarrassing aspects of romance' part that I wrote in the previous post?

After she declares Ichika her "Bride※1," she regularly sneaks into his room at night in order to sleep together with him (I mean literally... she just sleep next to him... nothing naughty happens...), and Ichika usually finds out about the break-in when he wakes up in the morning - to find Laura sleeping next to him... totally naked※2 (she doesn't have pajama and is accustomed to sleep naked, saying 'It's more comfortable not to wear anything when sleeping.')

In that sense, Laura is way ahead of other heroines in terms of exposure... (almost on par with Charlotte)

As the story progresses, Laura eventually begins to learn about the 'embarrassing aspects of romance' and starts to show signs of blushing or overreacting with strong 'Tsun' elements.


※1
The correct word in this case would be 'husband' instead of bride, but she lacks common sense and worse, was educated by her lieutenant(now an acting-commander of the special force unit in German) before she transferred, learning a somewhat twisted Japanese culture where the method of proposing to a loved one is 'I'll take you as my bride' - apparantly regardless of gender.
This is due to the lieutenant being an avid fan of Japanese shojo(Girls') manga, where the frequent love propose would involve a prince charming telling the princess(or heroine) 'I'll take you as my bride.'

※2
Well, except for a black thigh-band that she always wears - it's the close(in standby) form or her IS.

http://i20.photobucket.com/albums/b2...0157292021.jpg

http://img822.imageshack.us/img822/8...3e39d82040.jpg