The Testament of Solomon, an early treatise on demons of Judeo-Christian origin, presents the demon Ornias, who assumes the shape of a woman to copulate with men (though in other versions he does it while in the shape of an old man). After meeting him, king Solomon asks Beelzebub if there are female demons, suggesting a difference between male shapeshifting demons (incubi/succubi) and genuine female demons.Similarly, angels in Christianity have also masculine genders, names and functions. For example, the Grigori, led by Azazel, descended on Mount Hermon and copulated with earthly women out of lust, having children with them.
Plutarch wrote that demons could not feel sexual desire because they did not need to procreate; his work inspiring later Remy's opinion. Thomas Aquinas asserted that demons could not experience voluptuousness or desire, and they only wanted to seduce humans with the purpose of inducing them to commit terrible sexual sins. Remy wrote that "demons do not feel sexual desire inspired by beauty, because they do not need it to procreate, having been created since the beginning in a predetermined number". Boguet said that demons did not know lust or voluptuousness "because they are immortal and do not need to have descendants, and so they also do not need to have sexual organs", so demons could make people imagine that they were having sexual relationships, but that actually did not occur. Vignati agreed with Boguet saying that sexual relationships with demons were imaginary, a mere hallucination provoked by them, and Johann Meyfarth agreed too.
This argument derives from messianic interpretations of the Old Testament, which hold that humans need deliverance from Yahweh's judgement because of sin, claiming that demons only attempt to stop humans from having faith in a messiah, and can achieve this without mating with humans.
Rias is the woman who reincarnated Issei after Raynare killed him and the woman he loves. When she first summoned him, she treated him as a "special" case, knowing that he had a lot of potential. Issei was attracted to her like any other girl but disliked her for forbidding him from associating with Asia for being on the Fallen Angels side and saving her from them, that is until she realised that they were up to something shady in their town. After helping him save and resurrect Asia as well as killing the woman who murdered him, Issei began developing more respect and admiration for Rias to an eventual crush. In Volume 2, as time went on, she later started to fall in love with him and her love became deeper after he saved her from Riser and for recognizing her as an equal rather than an heir of Gremory or a Devil. She kissed Issei for the first time, following the latter's duel with Riser. She often gets jealous when other girls flirt with or tempt him, even saying that Issei belongs only to her. She loves him very much and is willing to do anything with him. In response, Issei will do anything to protect her, as he loves her just as much as she loves him.
When Akeno first met Issei, she thought of him as a cute kouhai with whom she could spoil and flirt, but as time went on, she started to see that Issei was very kind and caring. She began showing lustful attraction towards him after witnessing his determination against Riser. His kind acts were fully shown when he defended Akeno against Kokabiel's insults towards her heritage which eventually cause her to completely fall in love with him in Volume 3. She isn't afraid to get into fights over him with the other girls as she loves him just as much as they do. She does get jealous when other girls get closer to him, though she is a lot calmer about it than Rias and the others.
In Volume 7, upon going on their date, she loses her "Onee-sama" aura around him and acted like a normal girl her age, which Issei admired a lot. When the thought of Akeno someday getting a boyfriend popped into his head, Issei was determined to make the best of this so that he would be jealous of Issei. Their date eventually led to a street of love hotels while trying to escape their friends pursuing them, Issei was on board with going in having sex with Akeno when she assures him that she didn't mind, however their date came to an end when Odin and Akeno's estranged father arrived. During this time, Issei would learn about Akeno's past in more detail concerning her mothers death and how she blamed her father for it. Understanding her pain Issei attempts to help her overcome this, later going as far as to resist having sex with her as it would've further complicate things, instead he simply gave a gentle embrace, showing how serious she means to him. Near the end of the battle of Loki, Issei was able to reconcile with Akeno with her father, this led Akeno to both kiss and confess to Issei that she loves him in front all the other girls.
In Volume 10, during the preparations for the school festival, Akeno scolded him when he unknowingly hurt Rias' feelings by not calling her by her name and not acknowledging their relationship. She later came to comfort Issei when she figured out why Issei was unable to confess to Rias and would look at the ORC girls with frightened eyes, saying that she likes him and that as a Fallen Angel herself, she can replace Raynare who hurt him. She told him to have more confidence as she could not take another step forward in her relationship with him until he confessed to Rias, as she promised to stay with him forever. She later peeked at Issei's confession to Rias, saying that she can get serious about having an affair with him.
In Volume 22, Issei both confessed his love for her and proposed to her through the broadcast of the Rating Game between his team and Baraqiel's team, during his final fight with Baraqiel. After the events, Akeno has constantly been calling Issei "Darling" and started behaving like she is his wife, despite being only engaged to one another.
She started to develop feelings for him after he helped her overcome her fear of Senjutsu, as Issei told her he was not afraid of her powers and would stop her if she ever went out of control. After that, she began sitting nowhere else but on Issei's lap, and began seducing him like all the other girls in the harem. While Koneko still dislikes his perverted ways, she appears to still love him in spite of that and doesn't mind if it's directed at her now. She often gets jealous like the others if another girl is displaying any sort of affection or acting intimate with him. Still, whenever Issei says something that implies he is not a lolicon, she gets mad at him.
After Issei went into Juggernaut Drive (and after his return in Volume 12), Koneko has been having Senjutsu healing sessions with him in order to restore his life energy that was lost. During one session, she tells him that she would hate it if he died and that she would keep doing these sessions for the rest of her life if that was what it would take, making him promise to never use that form again. She offers a faster method to heal him, though it would involve them having sex, and a flustered Issei rejects the offer, as he wanted Koneko to be with someone she loves (as he still believed the girls around him didn't like him during this time).
In True Volume 2, she showcased her newfound boldness as she joined Akeno in dragging Issei into Akeno's lust room to spoil him before departing for their training camp, even to the point of being willing to have sex with him along with Akeno before they were interrupted by the other girls.
Kiba is the Knight of the Gremory group and best friend of Issei. In the beginning of the series, Issei is extremely jealous of Kiba due to him getting all the girls' attention with his good looks and had strong feelings of animosity towards him. Eventually, Issei started to think of Kiba as a good friend after spending time together with him whilst training and talking about their futures together. They both want to become strong so they can protect the girls of the Gremory group. Issei and Kiba have a good friendship and are willing to protect each other from harm. When Issei died, Kiba felt sadness and anger but kept it in. He released his anger on Siegfried, although losing but gained strength when one of Issei's Evil Pieces turned into Ascalon for him to use. Like the others, he gained hope when he found out Issei's spirit was alive.
Issei also worries about Yuuto due to not having a girlfriend despite his handsome looks and popularity with females, to the point of trying to get him together with Tsubaki Shinra, much to Yuuto's confusion. Issei feels that Yuuto is far too reckless at times and by having a girlfriend, he wouldn't be as reckless.
In Volume 18, it is revealed that Michael has crafted a special room that is located in a different dimension that would allow her to copulate with Issei without fear of falling, much to Irina's embarrassment. Irina and Issei spend some time together in the special room in which they reflect on their childhood and they become quite intimate before being interrupted by the other girls. Later on in the Volume, Issei states that no matter what, Irina is his childhood friend and is someone precious to him, much to Irina's happiness. At the end on the Volume, Irina kisses Issei in the snow. It is also revealed that she was Issei's first kiss when they were children.
She wants his genes as the Red Dragon Emperor since she wishes to give birth to strong children as a way of making up time she feels she lost as a woman while in the service of God, rather than out of any romantic feelings she has for him. That changes after she begins to fall in love with Issei when he expressed his opinions to Michael to provide convenience for her and Asia to be able pray to God without experiencing the pain that came along with it. As the series progresses, it is shown that Xenovia has developed genuine romantic feelings for Issei due to his determination to protect his comrades even if he gets injured by doing so. She also emits a scary aura whenever the other girls are getting closer to him. Xenovia has displayed concerns that the path to being with Issei is becoming farther as other girls get closer, causing her to be more aggressive in seducing him, shown in Volume 16. Despite having difficulties understanding her personality, Issei is willing to protect her just as much as the other girls. 2b1af7f3a8