Responses
No, Kurose was not there. It was only Shirotani's imagination.
I also had a doubt at first but as soon as we could see Shirtani was indeed alone in the restroom, I understood Shirotani imagined what he wanted from Kurose and what was arousing him.
Was Kurose really in that restroom... in the begining I thought it was Shirotani using his imagination... but Kurose smirk in the last image makes me feel he is there... I don't think Shirotani can imagine Kurose face!!!