Poji X Kon (“Positive Complex”) [English], by 212

That’s a nice, simple and “efficient” (some clichés never get old ^^) release that Mikakunin has brought to us, thank you ! ^_^
The idea : a couple made of virgins isn’t making progress, so the girl’s elder sister joins and kickstarts a threesome, followed by the obligatory “boyfriend-kun’s penis belongs to me !” line. Even with the censorship, even with this old canvas, it works well, the two girls are cute in their own way (bashful self-confident busty older sister, shy pettanko younger sister) and the boy isn’t a scumbag ruining it

–Update: excellent news, this share has become obsolete!
You may now find its contents inside the excellent Aimitsu Carameliser, a wholesome 228 pages long complete volume