Reading the novel and the adaptation seems to skip content near the end. Skipping and altering scenes. (e.g Teacher doesn’t send him the red gem to eat via. mail; Karyan’s the one to give to him directly.)
And I believe there were another couple of chapters that were left unadapted (chapters that weren’t part of the Epilogue/extras, I mean). I can’t tell what the extra chapters actually entail, though, so I’m not 100% sure on that part.