Notes: Unbetaed. Spoilers up to volume 14, ch 62. Set at the end of chapter 62.
There are two things Shuuichi keeps in mind whenever he is dealing with Natsume. The first is that Natsume is only sixteen, and the second is that Natsume will sacrifice himself equally for his close friends, casual acquaintances, youkai, and even his enemies.
Shuuichi is a great mimic. He studied how people interacted for years – reading books, watching movies, watching people until he had their interactions down enough to embark in his own interactions. His handsome face lets him get away with the small mistakes at first (though Shuuichi has always thought his looks were marred by the lizard tattoo which crawls carelessly across his body), until he no longer makes mistakes. And now it is second nature to don a mask which is much more natural than the one Natsume presents to the world.
He didn't keep it up very well when he heard the youkai call Natsume "the famous Natsume". He was neither stupid nor unobservant. He knew that Natsume carried something with him everywhere that he was careful to never show to anyone. He also knew that Natsume had a lot more interaction with youkai than anyone, even exorcists.
There is a truth that Shuuichi only takes out and examines on nights when he is back in his sparse apartment. That truth is that due to a lifetime of being hounded by spirits, Shuuichi is just as bad with people as Natsume and he has very little idea of how to be a good friend.
When he first met Natsume, his only thought was to take advantage of the boy's spiritual power, either as an apprentice or a tool. He tricked Natsume into that hot springs/exorcism trip, and it was only after he was forgiven for doing so that he understood enough about Natsume to know that all he ever really had to do if he wanted to use Natsume's power was ask.
Contrary to what Natsume thinks, Shuuichi is not a kind person. He daydreams of all he could do with Natsume's power at his disposal. But he also daydreams of what it would have been like if they'd grown up together. He does not know what a good friend would do, but he does know what a big brother would.
So he stops asking.
He offered sanctuary, and quietly started to protect the territory around Natsume. Because although Natsume's flinches could easily be contributed to growing up bullied by youkai, Natsume's attitude that every other person was more important than Natsume himself made Shuuichi want to follow the chain of foster homes back until he found which home (or homes if he was being honest) taught Natsume that he wasn't special, and that he must hide so much of himself to survive. Luring a misfortune demon to those houses would be child's play after that. Or maybe Hiiragi would want a chance. She was fond of Natsume in her own way.
Because Shuuichi doesn't doubt that if Natsume had grown up in a loving, supporting family, there wouldn't be a creature alive who could stand up to him. Natsume shows such moments of passion, leadership, and charisma that it hardly came as a surprise to Shuuichi when his research turned up the names of several youkai who would flock to Natsume's side. It's incomprehensible to Shuuichi that they'd do so without a contract, but he supposes it is easy for them to become fascinated by a child who can see them.
Shuuichi had been shocked when his shiki reported the ugly cat that was Natsume's shiki in all but name was extremely powerful and feared by most youkai. He had worried that the cat would turn on Natsume, but their interactions have assured him Natsume will not be willingly betrayed. However, there is a fear which drives all of Shuuichi's interactions with Natsume; he fears that one day the cat will be too late - that Natsume will not live to grow up.
Natsume will not stop jumping into youkai and exorcist business. Shuuichi tries to take care of any issues near where Natsume lives before they reach Natsume, but Natsume draws youkai to him. It's a toss up whether his recklessness or his kindness will be what will get him killed, but if he continues at this rate, Shuuichi is truly uncertain about Natsume's chances of reaching adulthood.
And now he has learnt that there is something in Natsume's possession which, if it is anywhere near as famous as Natsume's name appears to be among youkai, makes Natsume's chances of survival sink lower every time Shuuichi's imagination conjures a new, potentially terrible artifact for Natsume to be protecting.
He is of two minds on the matter. Up until now he has chosen to be a good friend and not mention the things Natsume keeps hidden. A good friend would continue to leave the issue alone. But increasingly, he finds he doesn't care if Natsume hates him, so long as Natsume is safe. Or perhaps the more cynical side of him is banking on what seems to be Natsume's infinite capacity for forgiveness.
Either way, he allows himself a small sigh once Natsume is gone from Takuma-san's house, then pulls his mask on tightly. His voice is carefully blank when he orders his shiki to investigate what it is that Natsume is always carrying. He will do whatever needs to be done to ensure that Natsume will grow up because while Shuuichi is not a kind person, he finds that for Natsume, he's is capable of being terribly kind.