The 'akaza sad story' might refer to the tragic backstory of Akaza from Demon Slayer. Akaza was once a human with a strong will. He had a family and a normal life, but due to various misfortunes and being turned into a demon against his will, he lost his humanity and was forced to do cruel things. He also had a lot of inner struggles as he still retained some of his human emotions deep down, which made his story a sad one.
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 Akaza x Douma NSFW comic is probably of a mature nature, featuring sensual or risque situations with these two characters. It may not be suitable for all audiences due to its adult themes.
Well, Akaza, originally Hakuji. He was a kind - hearted young man at first. He got involved with some bad people who took advantage of his situation. His love for the girl was pure, but they couldn't be together. When he became a demon, he lost some of his human memories but not all. His back story is full of pain and loss, which in a way, shapes his character as a demon. He is a complex character with a past that has both human and demonic elements intertwined.