They're Fallen Angels not Demons.
There are DEMONS aside from ANGELS. Didn't you read it? Even the summary says it all about ANGELS AND DEMONS. If you will correct me, make sure to show the page proof.
(︶︿︶)＝凸
The black wings and he calls himself a fallen angel.
http://www.mangago.me/read-manga/daten_no_tsuki/mf/v01/c001/42/
How will you explain this to me?
http://www.mangago.me/read-manga/daten_no_tsuki/mf/v01/c002/12/
http://www.mangago.me/read-manga/daten_no_tsuki/mf/v01/c004/3/
They've used the word DEMON in these two pages and more. THERE ARE DEMONS IN THIS MANGA. Accept that and stop correcting people who have BETTER comprehension than you.
My goodness! Can you read my comment? I've said ANGELS AND DEMONS with both "s" which refer to SOME characters. I didn't focus my comment on the first main characters. I'm commenting in general aspect.
It was a good tail of demons and angels. Just a bit confusing if you will not start at the beginning. ^^