Tone can be very tricky. But sometimes we get lucky and the author will come right out and explain the tone, often in the hands of a smart interviewer. We get a version of this in the interview with Jay Asher found in the 2007 paperback copy of Thirteen Reasons Why. When asked if there is a "message" behind the novel, he responds:
Basically, even though Hannah admits that the decision to take her life was entirely her own, it's also important to be aware of how we treat others. Even though someone appears to shrug off a sideways comment or a rumor, it's impossible to know everything else that's going on in that person's life and how we might be adding to his/her pain.
This message seeps very deeply into the tone of the book. Sometimes it's pretty direct, like when Hannah tells people that if they'd acted differently, she might not have been led to take her own life. Sometimes it's a little more subtle:
I'm listening to someone give up. Someone I knew. Someone I liked.
I'm listening but I'm still too late. (8.281-282)
Through Clay's words, Asher reminds us – the readers – that we can't wait until it's too late. Be sensitive. Act now. (Or we might end up in Clay's position.)
Because we know from the beginning that Hannah has taken her own life, all of the stories we hear are very ominous. We have to sit through all of these stories, knowing that every single one played part in why this young girl committed suicide. It's almost impossible to enjoy the stories, even when Hannah recalls a sweet or tender moment. Ominous, indeed.