Hm, I think the death that actually astonished me was Nagito's. Wasn't necessarily expecting Chiaki to die, but she seemed just as vulnerable to death to me as most of the cast, while Nagito seemed practically untouchable (which, I guess in the end, he was). The other would be "Byakuya", because I obviously wasn't aware of the Ultimate Imposter stuff and I certainly wasn't expecting a survivor from DR1 to be the first to die, especially when he had certain plans in regards to the traitor and the mystery surrounding the island.