When Asia first discovered that Issei was a Devil, she still held strong feelings towards him and didn't mind turning into a Devil as well, so long as she could stay together with him. Whenever Issei thinks of anything perverted or behaves in a lecherous manner towards another girl, she would often get teary-eyed and pull his cheeks. Though she realizes that Issei is in love with Rias, she doesn't give up on her desire to be with him. Asia's relationship has developed from a younger sister's love to that of young lover. She has also stated that she wishes to bear Issei's children in the near future. Her feelings have grown from an innocent love to a more serious relationship.
Asia cares for Rias like a sister even though she knows that Issei loves Rias. She will not give up on her love for him and stated in Volume 9 that she wants to have kids with Issei in the near future.
Asia and Xenovia are best friends. When they first met in Volume 3 there appeared to be some tension between the two after Xenovia showed her disgust at the holy maiden who had been turned into a Devil. However, since then, everything has changed for them after they spent some time together and shared some common interests. Asia and Xenovia are often seen together praying but Asia treats her as a love rival since Xenovia is often trying to seduce Issei into doing naughty things.
Asia, Xenovia, and Irina are called the Church Trio by Issei because they are often seen praying together. Asia considers her a great friend. Asia also sees her as a love rival and fights with her, along with the other girls, for the Issei's affections.
Raynare took Asia's Sacred Gear but was defeated by Issei and terminated by Rias. Rias returned her Sacred Gear to her and reincarnated as a Devil to become a member of her peerage.
At one time, Asia was an ally of Freed after she was banished from the Church. Even so, Freed was abusive towards her, and Asia feared him. He even took part in the plan of removing her Sacred Gear, knowing full well that the process would kill her. They have since become enemies with her transformation into a Devil.
Asia has developed a relatively close relationship with them and has seemingly been adopted by the couple as surrogate parents (and future in-laws).