
I am thinking of a theory that Alto's father may be one of the kannagis and even the longest living one before Elva (8 years). And, when these two met, Alto was 13 years old while Elva was 18, 5 years ago when Elva first started his kannagi job, Alto was 8 years old. If Alto's dad is actually the 8-year kannagi, it means he became a kannagi around the time Alto was born, it could be related to his nostagic feelings of the black ocean, like he inherited some memory / experience from his father?!? It could explain why those black ocean things are harmless to him?
Or, I might let my imagination go too wild =))))))

IKR. Also her mother's limbs didn't blackened or anything.
That's why it's a secondary theory... I'm more towards the 1st one: the Alto's mother's death could be a big part in the story. Not only because it was the trigger/reason why Alto stays with Elva (her parenting method got him to be that kind of a person, the loss that had a big impact on him not wanting to lose someone important anymore, Elva reminds him a lot to him and his mom's relationship, etc.), the death or his mom herself could be a foreshadow to something else that will be unleashed in the future.
Or maybe I just overthink a background story as a foreshadow.....

Yeah, reincarnation does not seem to sit well with this story.
Btw, we can not forget about the song Elva sang, it seems Alto also knows that song for some reason, and the butcher knife that was left behind by his father might have something to do with the plot also.
I have a feeling that every little details in this story has been thoroughly thought and taken care of(づ ̄ ³ ̄)づ
this is really good! so interesting!
Alto said that it was "nostalgic" when he was drenched in seawater...hmmm...maybe he has a connection with those "creatures" from the sea?
Also "animal therapy"? so cruel... but it was funny...