Raynare was Issei's first girlfriend, under the alias of Yuuma Amano. But the only reason she dated Issei was to kill him in order to destroy the Sacred Gear hidden within his body. Issei told her that she was his first girlfriend when Raynare mocked him and tried to kill Asia. Issei prayed to Satan to punch her at least one time. However, Raynare only laughed because she falsely believed that Twice Critical, the Sacred Gear that she believed Issei was the host of, would be no match for a "strong" Fallen Angel like herself. It was her words that caused him to stand, not minding the pain caused by two light spears that were stabbed in both of his legs, as he managed to unlock the first of many forms Boosted Gear had to offer. Realizing that the Sacred Gear she underestimated wasn't a Twice Critical as she thought, but rather a Longinus, she tried to run away from Issei in desperation. However, this effort was thwarted as Issei grabbed onto her immediately and punched her, defeating her in one hit. Just before she was about to be executed by Rias, in a failed bid to appeal to Issei's heart, she transformed into Yuuma and begged him to save her. Realizing what she was up to, Issei surpressed his feelings and had her killed by Rias nonetheless.
In Volume 10, it was explained by Asia, Akeno, and Koneko that Raynare had left a "curse" on Issei's heart, just before she died. The scar in Issei's heart made him fearful about getting too close to women as he thought that they would reject and ridicule him just as Raynare did on their first date. The trauma that Issei received prevented him from confessing his love to Rias. After a heartfelt healing session, the girls quickly object to this and the "curse" was slowly lifted.
Raynare never cared for Asia. She only wanted to take the Sacred Gear Asia had in possession so she could appeal to the Fallen Angel Leaders that she looked up to: Azazel and Shemhazai. She did not care about the fact that Asia would lose her life in the process. Asia was just a tool that she tried to use so that she could obtain Twilight Healing.
Raynare worshiped Azazel and it was her drive to be of better use for him that led her to kill Issei and steal Asia's Twilight Healing, thus, paving way to her own demise.
Raynare worshiped Shemhazai as much as she did with Azazel.