Akeno is madly in love with Issei but she isn'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 will 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. After Issei's victory over Riser, 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, when Issei tells Akeno that he likes her despite her Fallen Angel heritage, her feelings for him become more romantic in nature. 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 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 help 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 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 so, 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, cares a lot for Akeno since she is the daughter of his good friend Baraqiel and he subsequently treats Akeno like his own daughter. After Akeno reconciles with her father, Akeno and Azazel's relationship also improves over time. In Volume 12, Azazel gave Akeno bracelets that brings out her fallen angel potential, which she used to overpower the Khaos Brigade. As time progress she no longer have doubts towards him and as well as treating Azazel as her second father, but she will not hesitate to punish him he does clumsy things.
The two get along quite well with each other.
The two are shown to have a good relationship and get along quite well with each other.
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, Akeno and her father were reunited. Baraqiel later trained Akeno in using her Holy Lightning.
Akeno had inherited her sadistic side from her mother, Shuri Himejima, whom supposedly had performed SM acts every night with her husband, Akeno's father, Baraqiel. It is implied that she also has a masochistic side that she inherited from Baraqiel himself.
Akeno met Venelana shortly after she arrives at the Gremory Palace. 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".
Akeno was very close with her mother and loved her mother dearly, as such 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.
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.