Akeno is madly in love with Issei, but she wasn't his official girlfriend because he loves Rias. Akeno cares a great deal for Rias and does not want to destroy her relationship with Issei, but she does declare that she would be Issei's mistress.
When they first met, they were on good terms with one another, as she helped Issei get accustomed to being a Devil, such as teaching him to use his demonic power. She also enjoyed teasing him and didn't mind whenever he saw her naked. After Issei's victory over Riser Phenex, Akeno develops feelings for him due to how manly he was fighting Riser in both the Rating Game and in the engagement party, though these feelings were more akin to lust than love. However her feelings for him become more romantic in nature when Issei defended her from Kokabiel's insults towards her half-blood, and later on he tells Akeno that he likes her despite her Fallen Angel heritage,. It is after this point that she becomes much more seductive towards him and desires to be physically intimate with him, to the point of having sexual dreams about him, while also displaying jealously if other girls get closer to Issei. She tends to get aroused whenever Issei displays his manly side, such as when he confronted Diodora Astaroth for trying to make a move on Asia. It is also at this point that Issei becomes a source of comfort, as his kindness and courage helped her to overcome her hatred of her Fallen Angel blood.
While acting like a mature woman at school and being seductive towards Issei, Akeno also has a hidden personality of a girl who is innocent and shy when it comes to love, which she displays only around Issei. When on their date, she behaved more like a normal girl, and she was much more shy when offering to be physically intimate with him than she had in the past.
After Issei helps Akeno reconcile with her estranged father, her love for him deepens greatly, as she openly confesses that she loves him in front of the other girls. She becomes more psychologically dependent on him after this point, as Issei has the ability to (unwittingly) affect her mental state. Prominent examples include when she became enraged when Issei loses in the Rating Game against Sona Sitri, when she became greatly saddened when he was going to leave her for a few days on a trip to Kyoto, and when she became detached from reality after Issei's 'death'.
There are times when Akeno will fall into a depression if she believes that Issei has truly been taken away from her, and that she has no chance to get him back. This occurs when Rossweisse asks Issei to be her boyfriend, and when Issei was taking a bath with Grayfia. Akeno has stated that she would love to bear Issei's children during the visit of Milicas in the human world.
In Volume 22, Akeno was confessed and proposed to at the same time by Issei through the broadcast of the Rating Game between her father, Baraqiel's team and Issei's team, during Issei's final fight with Baraqiel. After the events, Akeno has constantly been calling Issei "Darling" and started behaving like she is already his wife, meaning she accepted his proposal and the two are engaged.
In Volume 23, Akeno would take even more bold actions such as calling Issei "Husband" or "Dear" and wash every part of his body when bathing together.
Akeno is Rias' closest friend, constantly being at her side after Rias saved her from being executed and accepting Akeno as a whole. Akeno eventually became Rias' Queen and first peerage member. Akeno is, in fact, close enough to call Rias by her first name in private while maintaining their master-servant relationship.
After moving into the Hyoudou Residence, Akeno starts to call Rias by her first name when in the house and the two constantly get into quarrels (such as pillow fights or using their demonic powers against each other) over Issei. Akeno is seen as Rias' main rival for Issei's affection, as both are the most seductive towards him, and their fights will sometimes cause the other girls to back off. Despite this, the two of them care greatly for one another.
Akeno cares for Asia like her own little sister. Asia also respects Akeno despite being love rivals for Issei's affection.
Koneko is Akeno's love rival for Issei. Despite this, the two are on generally good terms with each other.
The two get along quite well with each other.
The two are on good terms with each other, despite being love rivals.
The two are friends and Akeno looks after him as she does the rest of the Gremory Team.
Although love rivals, the two girls generally get along with each other.
Akeno initially didn't get along well with Azazel, who is a Fallen Angel like her father. Azazel, on the other hand, cared a lot for Akeno since she is the daughter of his good friend, Baraqiel, and he subsequently treated Akeno like his own daughter. After Akeno reconciles with her father, Akeno and Azazel's relationship also improved over time. In Volume 12, Azazel gave Akeno bracelets that brought out her Fallen Angel potential, which she used to overpower the Khaos Brigade. As time progressed, she no longer had doubts towards him, treating Azazel as her second father, but she would not be hesitant to punish him if he did clumsy things. Like Issei, she is deeply saddened after Azazel sacrificed himself in order to seal Trihexa, along with the leaders of various factions of the world, inside the Isolation Barrier, knowing that she is very fond of him by treating him, not just as a friend nor a teacher, but also a second father.
The two get along quite well with each other as they have very friendly terms to each other.
The two are shown to have a good relationship and get along quite well with each other. Akeno was very pleased to hear that she called her "momma" being related to the "father" who is Issei.
Baraqiel is Akeno's father. As a young child, it is suggested that the two were close, but that changed with the death of her mother, Shuri Himejima. Akeno blamed her father (later acknowledging that it was better to have someone to blame to preserve her own sanity) creating an estrangement between the two that lasted for several years. It wasn't until the pair met again in Volume 7, and with the support of Issei, that Akeno and her father were reunited. Baraqiel later trained Akeno in using her Holy Lightning.
Akeno has inherited her masochist side from her father, Baraqiel, who had performed SM acts every night with her mother, Shuri Himejima.
Akeno met Venelana shortly after she arrived at the Gremory Palace after Rias rescued her. According to Akeno, Venelana was the person who taught her the way a lady should act, different kinds of knowledge, and even studies.
Akeno has great respect towards Sirzechs as one of the leaders of the Devils as well as Rias' older brother. Sirzechs is shown to treat Akeno like his own sister, ensuring her well-being.
Akeno has been shown to have great respect for Grayfia, and is also a fan of the love story of Grayfia and Sirzechs.
Akeno is shown to be close enough with Millicas to call him "Millicas-kun". Millicas also treats Akeno like his own sister calling her "Akeno-neesama".
After moving into the Hyoudou Residence, Akeno has developed a close relationship with Issei's Parents, who she treats them as future in-laws, at times she competes against the other girls into gaining their favor. Akeno is particularly closer with Issei's mother, who teaches her some of her cooking recipes. Even after learning the truth about her being a Devil, Akeno's familial relationship with them still remand.
Akeno was very close with her mother and loved her mother dearly, as the events of her death left a scar in her heart, resulting in her hatred towards her father. Akeno has inherited her sadistic side from Shuri, as her mother had performed SM acts with her father, Baraqiel, every night.
Suzaku is Akeno's cousin and a niece of her mother, and the two have shown to lovingly know each other. Akeno calls her anee which proves that among all the members of the Himejima clan, she is the only one that she deeply cares a lot about. At the same time, Suzaku is very protective of Akeno, worrying about her situation during their separation in the past. Suzaku even allowed Akeno to return to the Himejima clan after she became the current head.
Not much is known about their relationship, aside from the fact that they have known each other as cousins and blood relatives. They have shown a certain degree of respect and are on friendly terms, and, at the same time, caring to one another. This is shown when Tobio sends Jin alone to assist Akeno against the Eastern Youkai faction. Akeno relationship with Tobio has become close enough where Akeno calls him big brother.
Akeno and Sona are shown to be good friends in their personal lives, calling each other by their first names when in private. They also go shopping together.