You-chan has boobs in this. Ahh, while I like Pito a lot (though I can't read Korean, curses), I wasn't too expecting anything great from this since I'm not a You-oshi, but as a piece of work, it was actually a fun read. It was cute, even if the sex scene was a little hard to understand. Chika-chan getting slightly upset was cute. Yea. Nyufufu.
Anyways, on the big argument ya'll are having over this stuff... well, I'm not stepping into the territory of what You wants to identify as in this doujin. I'll just drop a comment that I can agree with people saying it's not yuri sex, only because yuri sex is biologically female bodies going at it. It is however yuri if both parties in the relationship are girls, identify as female, etc. It's only the sexual intercourse that isn't for me.
(Because if I'm looking for lesbian porn, I'm not going for a penis. On that physical and sexual level, that's how I look at it. On everything else, girl to girl, any type of girl, is yuri. More or less.)