My Childhood Friends Mask Their True Nature Well ~BAD TRIP~

Even after Mei's relationship with Yuuki is found out, she continues her intimacy with Aki. And as the days pass by, his deviant demands of her escalate. One day, Aki teases her with sex toys and leaves her in her room to endure the pleasure while he attends school. However, worried that Mei hasn't been coming to school recently, Yuuki decides to pay her a visit... and thus witnesses her unbecoming display. The indecent sight of Mei wriggling and writhing while stimulated by sex toys should be maddening, and yet, Yuuki cannot withhold his desires for her. He reaches out to touch Mei and... After which, Aki returns home and bears witness to the two in the throes of passion, only to say: "Mei, that's not good enough. You must sway your hips in a way that pleases men more." And thus, the three fall endlessly in the depths of debauchery.

This is a sequel to Sotozura no Yoi Osananajimi. It depicts the BAD END flavored route where Mei ends up in a threesome with Aki and Yuuki.

(Source: DLSite)