Grope: Yami no naka no Kotori-tachi

The plots of the OVAs are quite different, but both are about a group of friends trapped in some kind of deadlock. Besides, in both situations the influence of the enclosed space is destructive, so the flow of the plot is somehow sad (nevertheless the endings do not match). 

Take the other guy's girl!! Rape,boobs jumping boob shots Dream sex 

Some 'vexing' sexual relationship.. 

Characters are very similar and setting is almost the same, except that Triangle Blue has a "good" ending. 

Both series tell stories of women who have weak will and gradually became sex slaves (due to influence of males who are aware of their weaknesses and they take advantage of them), betraying their feelings to beloved ones. Grope ~Yami no naka no Kotoritachi~ and True Blue have rather bad endings, especially for main male characters.