Kasshoku JK Onee-san To Futari De Ou-sama Game (“Playing The King’s Game With A Tanned JK Onee-san”) [English], an hentai doujinshi parodying the Sunohara-sou No Kanrinin-san series, by Hijiri Tsukasa
Until the last page, I thought that was an original work, and not a doujinshi. And yet, nope, it’s from Sunohara-sou no Kanrinin-san) ^^
Also, before I forget: if you liked it, it’s on sale for like just 3 bucks, here!
Here’s a bountiful release, in which a splendid teen gyaru (she’s got the whole package: slutty clothes including hotpants, beneath it a nanobikini, sexy tanned skin with tanlines and a heart shape on the butt, twintails, insolently proud breasts) takes a lucky shota to an hotel room.
There’s no scenario frankly, it’s simply good sex, the boy is irrelevant, only the glorious body of the girl mattered =)
Hellsin is the name of the guy guy who scanlated it, thank you!
By the same artist, Hijiri Tsukasa, circle Shin Seidou Honpo, I also share Takebe Saori-chan To Iu Kanojo To Ofuro Ni Hairu Hanashi, Tomoe Mami No Seikantai Mo Soul Gem and Takebe Saori-chan To Iu Kanojo Ga Dekita Hanashi.
And now, the download & gallery links 
Open the Complete Pictures Gallery
Download the Free Hentai Manga in a Zip file
(29 MB, 23 pictures, English)
I allowed myself to very slightly recompress the images before sharing. You won’t notice any difference with the naked eye, but now it’s only 29 MB instead of 158 MB =)
Or you can also use the Alternative:
Zip Mirror #1 – or – Zip Mirror #2 – or – Zip Mirror #3
Haven’t watched the entire series to date, but seems the key point is that young (literally) MC (Aki) is striving to “become a man”, yet seems to be surrounded by females, most of whom tend to have ‘shotacon’ tendencies.
And of course, in an H-doujin, said tendencies get (a-hem) seriously escalated, to the point where it’s almost natural to say to Aki-kun:

On sale in Japanese…
Well, yeah, if it were on sale in English, I couldn’t have shared it ^^
She was hot, the sex was not.
I agree with oldbrokenhand (below). But — that heart-shaped mark on her ass haunts me, floating before me even when I look away.