Shiori has something called Alexithymia, a mental health disorder subset that's characterized by a difficulty/inability to put feelings into words. It's common in victims of childhood abuse (though anyone can have it), which Shiori obviously experienced at the orphanage and then had compounded with each of his masters. Not only did they not nurture his emotional development, they taught him to ignore both his feelings and his natural instincts (trained to put himself into danger for his master without hesitation and to accept any and all punishments (even his life!!) from infancy) instead. This leads to a heavy dissociation from his mental state with a sort of numbing effect on his emotions.

Naga doesn't like that Shiori can't tell him when something is upsetting or scaring him which is why he keeps pushing Shiori. After Shiori's breakdown on the day Naga brought him to the shrine and again when he lowkey tweaked and told Shiori that if he couldn't figure out something he liked Naga would sell him, he's been very careful about how hard he pushes him so as not to detriment Shiori's emotional growth. Though Naga got him because Shiori is waaay better trained than the ever-aloof Mia and Marcus or the batshit crazy Danum, he didn't realize that Shiori (then 1802) was a slave because he'd only had limited interactions with humans and didn't know they actually had slavery until he had Mia investigate after seeing Shiori's brandmark.

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Nature spirits generally dislike and don't trust humans because they destroy the environment, but everybody on the island is fond of Shiori, the first human their master ever brought home. It helps that Shiori is so HECKIN cute and sweet, even if he does have a bad habit of reading every situation and doing what will make people happy. Even River would begrudgingly admit that Shiori isn't bad company, but only because he makes Willow happy.

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Master Xiao (remember that jerk Shiori was with at the beginning of the story? Yeah, him) questioned Naga's decision to build a koi pond because Naga is a large snake, and large snakes have been known to eat fish lol. Sorry, probably not as funny to you guys as it was to me, but I just imagined Xiao being like bro wtf you want the fish for? A snack?

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Shiori has had 5 masters including Naga. So far we have met Theodore, the second, Xiao, the fourth who Naga bought him from, and Naga. The others have been briefly been mentioned when Shiori is wondering how Naga will use him (Master 1 was mixed-use bedwarmer and bodyguard, 2 was bedwarmer, 3 was bodyguard, 4 was labor)

THAT'S ALL FOR NOW, PLS COMMENT QUESTIONS FOR A Q+A  if I can get 5+ I'll do one.