

Okay... He is an incubus since he is Male demon as what he really is. But this is a yaoi manga, fictional. So anything can happen. Author- san can do anything he/she wants.
Like this one ----- http://www.mangago.zone/read-manga/drip_your_heart
He is a MALE demon and is calling himself a SUCCUBUS.

Okay im just gonna clear your brain from that innacurate thought of yours.
A female and a male incubus both infest people on dreams. Yes they are similar.
BUT EVER HEARD ABOUT RULE 63? EVERY GENDER HAS A MALE OR FEMALE COUNTERPART.
Whether the lustful demon (male or female) feeds on dreams, semen or just piss. THEY STILL CLASSIFY BY THEIR OWN GENDERS (SO DONT BRING LGBT RIGHTS IN HERE)
And that manga you were talking about was just one single manga. How about
https://myreadingmanga.info/nokoppa-koakuma-ni-wa-sakaraenai-eng/
https://myreadingmanga.info/saiki-emika-koakuma-wa-ore-no-iinari-eng/
https://myreadingmanga.info/makuro-ash-wing-devil-kiss-eng/
https://myreadingmanga.info/sable-shingeki-kyojin-dj-incubus-holy-night-eng/
And theres a Genre called MPreg. Look it up.
Being a newly follower of yaoi you shouldnt assume too much by mangas. Since I study different mythologies I already accurately know their differences. Im not bragging im just helping you clear your shit up because that manga was a demo (fan) translation and some words in a certain language doesnt have an opposite gender translation for the other ones. (Like He,she on japanese translated to english)

Nope. Both uke and are male. Both of them will have sex with a man. If you're going for the second part of the meaning in oxford dictionary which says incubus a male demon who have sex with women, then both should be succubus! Those are just some mistranslation! If you view an uke as a woman, whats the point of reading yaoi then?