I wonder how hard would it be to catch the person without a shadow in real life. I mean, usually nobody would pay attention, but in the same time, it would feel wierd perspective wise, right?
That... Is more boring than it could be. Well, at least reasoning is expressed clearly.
Now then, if it was demonly demon the best solution would be tyranny - just force your way. But sweet bun that is Iruma doesn't really do that and he is denied of reasonable compromise of adjusting schedules...
Since Oni [with unreasonable exceptions] don't lie the only conclusion is there are bunch of gourds and Suika has different means to get drunk and mess with people in the process.