So in regards to Rui, I don't think as a child being turned into a demon and not having any guidance, I highly doubt he would be able to control his eating urges. The doctor demon was already older and probably had more handle on the situation and nezuko had tanjiro and his master and Giyu. Not that it's an excuse for him, but I do sympathize with him and all the other demons. But its like all evil baddies, they never truly start as evil, just circumstances that were beyond their control made them that way.
I really want to see more of the Giyu and Tanjiro communication. I feel like aside from being senpai, he's like an older brother to Tanjiro and wants to see him exceed, so much that he sent him to his master to train him. Also, I want Giyu to be the one to explain how to excel past the 10 forms.
They did mention in the beginning that it was about 2 years and change when he was training, which is why I loved the show because the time skip made sense and actually showed the training to get Tanjiro where he is today.
The next episode is going to be so dope because you get to meet the Hashiras and it looks like they will touch on how Tanjiro carrying a demon around will affect the corps. I wanna how the master feels about everything.