Issei Hyodo's first date with his new girlfriend ends poorly when she turns into a monster and stabs him in the stomach. Luckily, he's saved by Rias, the buxom president of his school's Occult Research Club. And then, things really start to get weird...

Surprise! All the members of the Occult Research Club are devils, including new-recruit Issei, who's having difficulties figuring out the whole "demonic power" thing. Maybe he'd have better luck if Fallen Angels stopped popping up and trying to kill him.

Issei meets and befriends a girl named Asia Argento, a Sister who has arrived to serve at the town's church. Issei learns more about the chess game in which he has become a part, and the roles that he and his fellow devils play within it.

Issei is determined to get stronger. He spends some more time with Asia, but once again, their circumstances keep them apart. Issei finds out that although pawns may not be very strong, they have a power that allows them to act like other chess pieces.

While Kiba and Koneko back him up, Issei rushes in to rescue a critically injured Asia. Leaving the others behind, Raynare and Issei become engaged in a duel to the death! Elsewhere, Rias and Akeno have their hands full with Raynare's fallen angels.

New living arrangements are made for Asia, who has been living in the club's room. Meanwhile, Issei begins a new training regimen with Rias to improve his physical fitness. Asia begins attending school, where she is placed in Issei's class.

Rias decides that it is time for Issei and Asia to have servant familiars. The school's student council visits the club room, and Issei learns that they are another faction of devils. The two groups compete to see who gets first pick of the new familiars.

Issei dreams that he is marrying Rias, which leads him to get in touch with his inner dragon. Asia confesses a desire to have a deeper relationship with Issei.

Issei and Asia undergo a special training camp with the other household members to get ready for the upcoming Rating Game. Issei struggles to figure out what his own special characteristic is. Rias explains more about devils and the Gremory family.

The time for the start of the Rating Game arrives, and the contestants are transported to a battlefield in an alternate dimension. While Asia and Rias remain at their base, Issei and Koneko face the opposition, and Issei reveals his new signature move.

Kiba becomes entrenched in battle against Karlamine, one of Riser's knights, while Akeno fights Yubelluna, his queen. Meanwhile, Issei takes on Ravel and the other remaining pieces. Rias launches an all-or-nothing sneak attack against Riser.

Issei wakes up to find that the battle is over, and he has lost. Rias and the others are at a party in honor of her engagement to Riser, but with some help from Grayfia and Asia, Issei decides to crash it, rescue Rias, and bring her home with him!

Issei is back with Rias and Asia living in his house, and Kiba starts acting weird when he sees a picture of a holy sword at Issei's house.

Issei gets another warning about the white dragon, and church followers bearing Holy Swords pay a visit to the devils.

Issei and Kiba fight the Xenovia and Irina, and Issei tries to deal with the consequences of their fight.

Issei and the others team up with the church to fight Freed, but an even greater enemy appears.

The Kuoh Academy students fight Kokabiel and his minions to defend their school and their town.

The Occult Research Club fights Kokabiel and learns some shocking truths about the power struggle between the angels, fallen angels, and devils.

The Occult Research Club takes over cleaning the pool to thank the student council for their help with Kokabiel, and Issei runs into a lot of trouble.

Issei learns more about the feud between the Twin Sky Dragons and Rias and Sona have to deal with troublesome family members at Open House.

The other Bishop of the House of Gremory is released, and Akeno takes Issei to meet a new acquaintance.

Issei meets Michael, the Chief of the Angels, and continues training Gasper in the days leading up to the Leaders' Summit.

Time stops during the Leaders' Summit, and Issei and the others meet a new enemy.

Issei battles Vali and discovers hidden depths to his power as the Twin Sky Dragons face off.

Summer break is coming up fast for Hyodo Issei, but all his plans are put on hold when he finds out he is to accompany Rias for her visit back home to the underworld! A new adventure is about to begin and all the while Koneko is not acting herself.

Issei and the others begin their training to improve each of their skills. All the while things are happening around them as powerful people gather to fight against the Chaos Brigade. All the young devils gather in one place.

Koneko's sister Kuroka has appeared to take her sister away from Rias Gremory. Issei and Rias chase after her to stop that from happening. At the same time, a figure who objects to these alliances between mythologies appears at the great gathering.

Loki has been sealed away, but only temporarily. Rias and her family are among the volunteers trying to hold him back, while Odin returns North to retrieve the powerful hammer Mjolnir. Will everyone be able to stand up and fight against a god?

With Loki defeated, Rias and her household return to the human world to finish up their last days of summer. A pile of homework awaits Issei, but he goes on a date with Akeno instead! Akeno throws herself at Issei, hoping to forget her terrible past.

Issei and the others are back to school and their daily lives. Irina and Rossweisse both start to live at Issei's house and the sports festival is fast approaching. During all of this, Diodora Astaroth appears before Asia and proposes to her?!

Diodora continues to pester sweet Asia as the Rating Game approaches. Issei and the others prepare for battle as dark things brew in the background. When the Gremory household jumps to the field, they find themselves in an unexpected battle!

Rias and her household leaves the fighting of the Chaos Brigade to the adults as they rush toward the temple to save Asia. There, Diodora replaces the Rating Game with a little game of his own. They must fight against his forces to get Asia back!

The sudden death of Asia surprises Issei and makes him trigger Juggernaut Drive. While Rias and her household try to save him, Azazel and Sir Zechs meet the leader of the Chaos Brigade! What is her true intention for creating the organization?

Asia saves Issei by healing the dragon within him after his incomplete transformation. Finally, they all make it back home and enjoy their peaceful days. After Loki fails with Issei, he turns his evil grasp toward Rias.

Issei goes to see Vali for help, which is in itself an action against the underworld. With the help of Arthur and his Holy Royal Sword Collbrande, the Rias household goes to the Dimensional Gap. There, they meet Rias and try to bring her back.

Issei must stop Rias by fighting against her. As she pummels him with attacks, Issei recalls various memories that he shared with her. Unable to leave Rias in such a state, he runs forward to bring back the regal and dignified Rias he remembers.