Kyonyuu Fantasy

You love the idea of a succubus? (maybe without the part of draining till death), then look no further both of these feature vanilla stories with succubus and all the great things that that implies, the second part of Koakuma Kanojo also has futa and the second episode has elf (which goes well with the fantasy theme of Kyonjuu Fantasy), take that into consideration, but the point of focus is the succubus and fantasy elements in these series. 

Both are hentai that feature a cute sexy succubus (well in Itadaki! Seieki the Succubus is half vampire, but it's still the same kink and roleplay), that changes in accordance with the lust of the protagonist, sure in Kyonyuu Fantasy there's more girls at play and is more fantasy oriented, but they're both great succubus hentai. 

Both OVAs have a fantasy setting in which the story takes place and it mostly focuses in vanilla for a single protagonist, there's also things like the character designs being reminiscent of one another, like the generic hentai protagonist, the similar body proportions to the females, the dark skinned beauty, etc.