This is a short anime episode during the events of Grisaia no Kajitsu. It centers around Yumiko Sakaki, and her personal fantasies in a bunny outfit in her room.
Although Yuuji is seen in this episode, he seems to be a simple illusion of Yumiko's. The reasoning behind his appearance might be due to Yumiko's growing interest of him during the course of events during the anime.
In the Blu-Ray DVD release of Grisaia no Kajitsu, there are 6 included special episodes, although these episodes can also be found among various anime sites.