Guys, there won't be any limit to harem members, and if you can provide me with your answers I can include some of the more difficult characters like Raynare, Kalawarna, and Mittelt, and some of the hostile Devils such as Katarea? However, it depends on if you guys if you want it or not.
Grayfia Lucifuge.
Venelana Gremory (married but still in obsessive love with MC since little), what do you think?
Rias Gremory
Akeno Himejima
Koneko Toujou
Irina Shidou
Xenovia Quarta
Rossweisse
Ravel Phenex
Asia Argento
Gabriel, The most beautiful angel in heaven.
Ingvild Leviathan.
Kuroka.
Genderbended Issei.
Serafall Leviathan?
Riser's Phenex Peerage as a one-time hook-up?
Roygun Belphegor
Le Fay Pendragon
Lavinia Reni?
Valerie Tepes
Yasaka
Tiamat
Nyx?
Jeanne of Hero Faction?
Ophis (Maybe).
Others (your answers).