This is a short anime episode, centering around Yumiko Sakaki. The episode consists of Yumiko and Yuuji hiding in a locker in the bath.
When Yumiko and Yuuji encounter each other in the bath, Yumiko hides with him as the other girls come to take a bath, as to not get the wrong impression about the two of them.
Trivia[]
Although this is a recollection from Yuuji for JB during a job promtion, it is unknown at exactly what time the events take place.
Source[]
Although it will later be part of the blu ray DVD release of Grisaia no Rakuen, these special episodes are still being created.