Unhealthy Burger

Go to the room on the left, before the stairs and sleep. The calendar advances to the next event then.

I played around with the gif too and got this image (flip it upside down and invert the colours). Maybe a character? Didn't recognize it, though.

So, uhm, talking about bugs, I found a rather interesting one in late game (Hiyoshi city) and haven't found another topic about it. Maybe counts as an exploit? Anyway, thought to inform the devs about it.