Yay! Casual guro is the best type of guro.
There's a little bit in this story that feels off though.
The teacher says: "If you're here for the graduation ceremony, the assembly hall is that way. Otherwise ... I must ask you to leave..."
But he is there for the graduation ceremony, so what's the problem? Why he needs Saaya to help him instead of just following the directions to the assembl hall?
You might have ment he needs an invitation to attend it, but I don't feel like it is transmitted at all.