But the only way to truly understand is to check out the manga:
http://www.mangahere.co/manga/kodomo_no_omocha/
Recently I found out that in celebration of the 10 year anniversary of the manga, the author, Miho Obama wrote a one-shot sequel with a cross-over of one of her Josei series. I'm not a fan of Honey Bitter which is the cross-over manga it's combined with but I love Kodocha and there was plenty of it in the book for me to be satisfied with.
And to see grown-up Hayama and Sana along with a quick peek at all your old faves, it was every fan-girl's dream. This is the stuff that no fanfics can ever compare to because the real author made it.
To read this sequel:
http://www.mangahere.co/manga/deep_clear/
Now I am going to have a link below of an image that I just anime style fell over due to emotion but I don't want anyone to click on it unless you're prepared for a spoiler.
https://s-media-cache-ak0.pinimg.com/originals/51/82/34/518234c3cc9c7d22d6c96d276001f594.jpg