GiyuTan (Smut) (Re-write)

Giyu Tomioka the water pillar, is told to go up the mountain to search for a demon. Giyu arrives a bit later and finds a red headed boy named Tanjiro. The boy tells him about his family being attacked.
Giyu then trains the boy to become a demon slayer. Tanjiro and Giyu become much closer and they now trust one another.
One day Giyu is sent to the mountains to kill a demon who is strong but not enough to be an upper rank. Giyu goes and doesn't return for days. Tanjiro is then called to the master's mansion for a meeting and is told that since he is the closest to Giyu he must go and try to find Giyu.
Tanjiro then goes as he is told. As he climbs the mountains to find Giyu, the air becomes thicker and he is struggling to breathe.
After struggling he finally finds Giyu, who is unconscious on the ground. He looks strange.
What happened to him? Was he attacked by the demon and killed?

Read more to find out!