Rias Gremory, she is the youngest daughter to the Gremory family along with being the little sister to the one of the current Lucifers, Sirzechs her older brother. Their father is both made of the Gremory and Bael.
Right now she is in a very terrifying predicament. Currently she is the Heiress the the Gremory clan along with being a Pure Blooded Devil she is in a forced marriage with a man she despises to her very core. His name is Riser Phoenix, a very prideful and playboy to the just as prestigious devil family, the Phoenix clan. Through many unsavory talks between talks between the parents the Phoenix's decided in order to preserve the pure bloodline they wanted a marriage between Riser and Rias. Much to the Gremory families displeasure they couldn't stop it as much as they tried. But the Phoenix clan still persisted with the marriage purposal.
With Rias being in this predicament she was given time to think on it. No matter how many times she refused the marriage still went as planned. Luckily Rias already has a peerage, and she thought about winning her freedom through beating him in a rating game, all she needed was her own type of Ace for her peerage that will be a pawn within her peerage. With great luck something landed in her lap, a boy who she kept her eyes on for awhile now. But whenever she looked at him her heart raced but also feeling a great power within him, his name is Issei Hyoudou the new Red Dragon Emperor.
As much as she wanted to save him from the fallen angel that was stalking him she couldn't pinpoint where that fallen was, it's energy signature went all over the place along with disappearing whenever her Rook Koneko would get close. She figured that fallen was using a type of magic hiding what she is along with making her go on a wild goose chase around town. And it's been nothing but an annoyance because she can't find where that fallen is hiding, not to mention its taken an interest in her new pawn in the future. She had to make sure she had to talk with him first before the Fallen can get to him.
Unfortunately it did.
The fallen angel was on a date with Issei but luckily her familiar was able to get a pamphlet to him she's very worried about his safety and being around a Fallen whom she doesn't trust and despises it was making her heart wrench. As much as she wanted to go in there, save him, and kill that Fallen that's been giving her the run around and she can't find her. The two were always next to each other along with being around alot of people. She can't go in or else it will cause alot of problems down the road that she'll have to deal with it, biggest hurdle for that choice is a fear of starting another war between Hell, Heaven and the Grigori or the Fallen Angels Faction for short.
After awhile of waiting Rias saw she was being summoned but she doesn't remember putting out any pamphlets, but it hit her, she gave Issei a pamphlet. Rias was teleported to Issei and he was literally down on the ground, her heart beat was racing on seeing him die in front of her. Originally she was going to lightly ask him to join but now she has to resurrect him with her pawn pieces.
Rias now hopefully has her Ace that will be able to get her out of the marriage with the most despicable man in the underworld. She wishing this is her chance to be free, and with some wishing she'll want to have a few dates with Issei, she doesn't know why but being around Issei makes her heart flutter. Now she just needs to train with her peerage to win against Riser.
Well, as much as she wishes to now spend time with Issei and her peerage members, the whole universe decided to go against her. Rias will soon see her greatest fear come to life and her dreams crashing down around her, all at the hands of Riser.
Weeks later Rias along with her peerage bonded with Issei and they also managed to find the Fallen Angel that killed him along with her followers. Issei was hesitant because before he also bonded with a young girl who's a nun and the two had a spark there but it was more of a brother and sister vibe at first. But after finding Raynare the Fallen Angel that killed him also killed the girl named Asia who Issei befriended but her body turned to dust and was no more.
Issei was hurt after losing a friend but Rias and her Peerage helped in his grief but soon after Riser comes knocking at her door with his marriage proposal.