I'm replying based on memory since no access to the game, but if I remember right, it should be the one with the maid costume? (I'm not sure since I forget the CG row number, but that one's the hardest to get so I'm assuming it is x'D)
If that's the CG you're missing:
Go to maid cafe with Toru, take the crossdressing job and MC & Toru will talk about a certain bet. Win the audition. Then, buy maid costume with size M on top of one with Toru's size. Make Toru wear the maid costume once (I think), then you will get the scene, but MC needs to be a bottom, if I remember it right.