Shuichi blames himself for every single death that happened in DRV3. Every. Single. One. Soon after the game ended and he was allowed to go home after his full recovery, he had nightmares about the victims dead bodies and the murders executions. He could barely stand it. He kept repeating the words, "I killed my friends." over and over again in his head. The only way he got passed that horrible period in his life was though the help of his boyfriend Kokichi, who woke him up from his nightmares and comforted him while he cried, his BFF's Kaito and Kaede giving him encouraging words of endearment, and Maki sharing her night terrors as well. He's so glad his friends are alive. He doesn't know what he'd do with out them.
