The Hashiras would likely show concern. Some, like Shinobu, would immediately start looking into possible medical solutions. Giyuu might be more reserved in his worry but would still keep a close eye on Tanjiro. The other demon slayers would also be affected. They look up to Tanjiro, so his sickness would lower the morale of the group. They would try to support each other while waiting for Tanjiro to recover.
He might be angry at first. Naruto has grown up alone and had to fight for acceptance. So when his parents say they regret abandoning him, he could lash out, saying it's too late. After all, he has already faced so much without them.
The son could ask for some time and space if he feels too overwhelmed in the moment. Then, when he's ready, he can sit down with his parents and have a proper conversation. He can also share some educational resources about homosexuality with his parents to help them understand better.
In some fanfictions, Naruto may become extremely bitter. He could feel a deep sense of betrayal and this might fuel his determination to become stronger, not for the sake of the village at first, but more for self - vindication. He might isolate himself from others and struggle with his identity.
In some versions of the fanfic, Harry might have a sort of instinctive understanding that his parents had a good reason for leaving him there. So, while he's still not happy about it, he might be a bit more accepting. Maybe he can sense some sort of protection spell around the Dursleys' house that gives him a small sense of security.
Some adults may feel extremely humiliated. They are no longer children and being spanked makes them feel as if their parents don't respect their adulthood. For example, they might become withdrawn and avoid family interactions for a while.
Tanjiro might use his sense of smell to detect hidden threats. Since his sense of smell is super - enhanced, he could sniff out any demons or traps in the way of saving Rengoku. For example, if there are demons disguised as allies, Tanjiro would be able to tell by their scent.