Now that I think about it, there's a lot of subtle things that may just deepen the story as it was.
Some chapters before, the class give a smile when they see Yugami and Chihiro talked again. Of course they're smiling when the plan to make them closer 'failed', so to speak.
Yugami using Russian, a language Chihiro doesn't understand to convey what he wanted to say without having to worry her misunderatood him. I mean, Heiraku also means a lot to him, and he's not Yugami's friend.
Heiraku finally telling the story Yugami wanted Chihiro to hear AFTER Heiraku saw Chihiro.
Now I'm sure the author also slipped something like these in the chapters before, maybe even from the beginning. Can we find them all?