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.
There are also fans who might be a bit nervous. They worry that the fanfiction they wrote might not be up to the standards that Dan and Phil expect. But overall, most fans are positive about it. They see it as a unique interaction between their idols and the fan - created content world. And this can lead to more fans being motivated to write better and more creative fanfiction in the hope that it might also be read by Dan and Phil.
The reactions would be complex. Kim's best friends would be in disbelief at first. They might question how this could happen so suddenly. Kim's parents would likely have a serious talk with her about the consequences and the future. Ron's friends might tease him a bit but also realize the seriousness of the situation. Ron's family, especially his mother, would probably start making plans to help them out. As time goes by, all of them would gradually accept the situation and offer their love and support to the young couple.
Well, Serena would probably be over the moon. She's always been close to both Dan and Blair and would see this as a wonderful union. She'd be there for Blair during the pregnancy, helping her with shopping for baby clothes and giving her advice. Nate, on the other hand, would be more practical. He'd offer to help Dan with any financial or housing arrangements they need to make for the baby. And then there are the more catty friends, like Penelope and Hazel, who might be jealous and make snide remarks about how Dan and Blair got pregnant so quickly, but deep down they're just envious of their relationship.
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.
The friends' reactions could be mixed. Some of them might be worried about how this pregnancy will affect Jack and Kim's future in martial arts. They could fear that the couple might have to give up their training or competitions. However, most of their friends would probably come around and be there for them. For example, their Sensei might initially be strict about their training schedule, but then realize that they need some flexibility during this time and adjust the training accordingly to support them.
Kim would initially be in shock but quickly shift to her problem - solving mode. She would assess the situation and start formulating a plan. Ron would be freaking out a bit, but he would also try to make light of the situation with his humor. Rufus would be exploring and might accidentally stumble upon some key information about the Chaos Gods. Meanwhile, Bonnie would probably be more concerned about how this chaos would affect her social status, but she might also end up helping Kim in an unexpected way.