AHHHH i know this manga but i can't remember the name! I dropped it.. ughh.
http://www.mangago.me/read-manga/aijin_incubus/
I think this is what you looking for if you havent already found it.
then is it this one its chapter four, i dont think its it but you never know
http://www.mangago.me/read-manga/kimi_no_nioi_ga_suki/mi/ee77140053c4b96ad12654d2e050e811_chapter-4/1/
ugh it might be it he did make a contract after sex, i should quit second guessing and let you decide if its the one.
http://www.mangago.me/read-manga/kimi_no_nioi_ga_suki/mi/ee77140053c4b96ad12654d2e050e811_chapter-4/1/
This is bugging me now too. The demon has long hair, very buff looking, and has long dark nails, while the boy was very scrawny and blonde looking. The demon was attracted to the boy's pheromones? Like sexually? Or something.
@Pinkypanda Yepp, this is definitely it. Good job on finding it. xD
I'm looking for a yaoi about this high school boy who meets a demon. The demon appears in the uke's bedroom when the uke is masturbating and the demon helps the uke climax. Then after that the uke can't get the demon out of his mind and one day during class the demon starts touching the uke because no one else can see the demon but the uke. Anyway, the demon later has sex with the uke and by doing that he forms a contract with the uke.
I know that it's a fairly new manga. I was just reading it and now I can't find it again. ;_;