I dont think komatsu will use his knife against a "friend" it just dont fits his char.
Toriko is just at the start of hi immersion career he needs to handle it to get slimmer , at least thats what I think..
Granny's creepy. I bet she somehow implants their opponents a bit of her "immersed food" , after that the opponent collapses cause their body cant handle it or he dies cause of hunger. Because the immersed food was to tasty and he suddenly wants more but dont gets it. Sounds kinda stupid lol hope you can imagine what I mean xd