At first it seems odd that Philip-as-narrator had the exact same voice as a sixteen-year-old as he has as a seventy-two-year-old. Then you realise: the main story isn't just a flashback, it's what Philip is telling Michiko in the Framing Device. Sixteen-year-old Philip isn't really narrating at all. (This also raises the interesting question of just how reliable a narrator Philip is, since he's describing events from fifty years ago.)
Fridge Horror
The first time you read the book, Hayato seems odd but not necessarily sinister until his treachery is revealed. (Even considering how Ho Yay-laden his interactions with Philip are, almost all of it is on Philip's side, and it's believable that a teenager would develop a crush on a teacher — especially a teenager as lonely as Philip.) But on a re-read he becomes downright horrifying. He befriends Philip while his family are away, quickly makes himself the only authority figure Philip trusts, and basically grooms Philip to behave as Hayato and his friends want him to.
Fridge Logic
Philip's flashback to his previous life raises questions — why does Hayato look the same in his previous incarnation? Did Philip also look the same, and if so, how? (A mixed-race samurai serving Tokugawa Ieyasu is... highly improbable.) Hayato remembering the exact same lifetime is equally odd — how was he able to recognise Philip when, as pointed out, Philip can't look the same?
