Asia, who has been living in the Occult Research Club's clubroom, moves into Issei's house to live with him. She and Issei begin getting basic training from Rias to improve their stamina, fitness and effectiveness during battle. Issei has trouble with successfully completing contracts for Rias, with his first client turning out to be a middle-aged, male, gigantic Magical Girl enthusiast named Mil-tan.
Issei dreams of marrying Rias, which leads to him hearing the voice of a Dragon in his head. That same night, Rias appears in Issei's room and begs him to take her virginity. Before he gets the chance, the Gremory clan's maid Grayfia interrupts them, telling Rias to leave with her. Rias regretfully does so, and the next day, the Occult Research Club are introduced to Riser Phoenix, an arrogant high-class Devil who Rias' father has chosen to marry her.
Not wanting to marry Riser, Rias suggests holding a Rating Game - a Devil tournament consisting of a battle between two Peerages. Riser then introduces them to his full Peerage, much larger than Rias' and all female. Seeing Riser flirt with and grope his [Queen], Yubelluna, despite being engaged to Rias, Issei is enraged and challenges Riser to a fight. He is easily beaten by Mira - Riser's [Pawn] and the weakest member of his peerage. Later, Rias takes the group to a mountain cottage to train for the Rating Game. While practising magic by peeling potatoes, Issei is inspired, and begins working on a new move with Asia's help. While Grayfia discusses Rias' choice to battle Riser with Sirzechs (Rias' older brother), Rias explains the history of the Great War before bonding with Issei. The next day, Issei's training has progressed to the level of being able to bast a hole in a nearby mountain during a sparring match with Kiba.
The battle is held in an alternate dimension containing a replica of Kuoh Academy. While Rias and Asia stay back at their base, the rest of the group attack Riser's base head-on. Issei and Koneko are ambushed by Xuelan (Riser's [Rook]), Mira, Ile and Nel (Riser's [Pawns]), but Issei is able to immobilise them using his new ability, Dress Break, before Akeno finishes them off. Disgusted by his move, Koneko walks ahead of Issei, but is caught by a surprise attack from from Yubelluna. Koneko tearfully apologises as her body fades away.
Issei is quickly informed that Koneko isn't dead, but has merely been teleported out of the game. Akeno starts to fight Yubelluna in Issei's place, as Issei regroups with Kiba, who has just confronted three of Riser's [Pawns] in the forest. The two take on the rest of Riser's Peerage: Ravel (Riser's [Bishop] and younger sister), Karlamine and Siris (Riser's [Knights]), Isabela (Riser's remaining [Rook]), and Ni and Li (Riser's remaining [Pawns]). Meanwhile, Rias has decided to take on Riser himself alone, but Riser appears to have the advantage. Issei learns that he can transfer Boosted Gear's accumulated power to one of his teammates - doing so with Kiba allows Kiba to use Sword Birth, transform the battlefield into a sword-filled deathtrap and killing all of their opponents except Ravel.
Very suddenly the tables are turned as a voice announces that Akeno has been defeated, while Yubelluna coordinates a surprise attack and eliminates Kiba. Now alone, Issei rushes to Riser's base and promotes himself (one of a [Pawn]'s abilities) to Queen. He tries to protect Rias by challenging Riser face-to-face, but due to his body having already reached its limit, he is bloodily beaten and almost killed by Riser. Horrified and unwilling to see Issei die, Rias forfeits, letting Riser win the Rating Game.
After hearing the voice of the Emperor of the Red Dragon - the Welsh Dragon, Ddraig - in a dream, Issei wakes up in his own bed, having fallen unconscious after the Rating Game. He is visited by Grayfia, who gives Issei a magic teleportation circle that will allow him to attend Rias and Riser's engagement party in the underworld. Before leaving, he asks Asia to do something for him and then speaks directly to Ddraig, who resides in his left arm, and asks to make a deal.
Issei shows up at the party, and Sirzechs agrees to cancel the marriage if Issei can defeat Riser in a one-on-one battle. On the battlefield, Issei reveals that he gave Ddraig permanent full control over his left arm in exchange for the ability to go into Overbooster by using Balance Breaker to grant him a full set of powerful armour - Scale Mail - for a full ten seconds (as much as his body can handle). This alone isn't enough power to defeat Riser, but Issei has another trick up his sleeve - holding it with his Dragon left hand, he punches Riser with a cross necklace he borrowed from Asia after pouring holy water onto him, inflicting enough damage to render him unconscious and win the battle.
Rias and Issei are flown home on a Griffin. Rias tells him that another engagement could come at any time, and Issei assures her that he would be willing to go through the whole thing again, giving his right arm or his eye. He is, after all, her pawn. Happily, Rias kisses him and later announces that she plans to move in with him and Asia.
Volume 2 of High School DxD contains examples of:
- Big Bad: The cocky, arrogant Devil prince Riser Phoenix, who treats Rias with no respect despite being engaged to her.
- Big Damn Heroes: Issei shows up at Riser's engagement ceremony just in time to challenge him to a duel.
- The Big Damn Kiss: The climax of the volume features Rias kissing Issei on the back of the Griffin.
- Chekhov's Gun: During the training camp, Asia shows the rest of the group a bottle of holy water she still keeps. Issei later uses that same water bottle to give Riser injuries he cannot regenerate from, getting the final edge in their fight.
- Chekhov's Skill: Issei training his magic by peeling potatoes and onions derives into him learning Dress Break, which he uses with great effect against four of Riser's pieces (and, in the manga, he threatens Ravel Phenex with the same if she tries to stop him).
- Crazy-Prepared: The final fight slowly reveals that Issei had coordinated an entire battle strategy beforehand - trading his left hand to the dragon living inside it so that he can activate Scale Mail and punch Riser whilst also holding a cross that he asked Asia for while pouring the similarly acquired holy water on his face.
- Cross Counter: Issei and Riser punch each other at the same time during the final battle. Though the hit seems to affect Issei more at first, Riser starts to bleed profusely when he realises Issei was holding a cross (making this a literal Cross Counter).
- Curb-Stomp Battle:
- Mira makes short work of Issei when he first meets Riser.
- The Occult Research Club curb-stomps most of Riser's peerage. Seconds later, Issei gets beaten up by Riser himself.
- Issei returns the favor to Riser at the end of the volume.
- Defeat by Modesty: Issei defeats Mira, Ile and Nel with his Dress Break.
- Determinator: Even at the end of his strength, and after Riser has beaten the crap out of him, Issei will not surrender. He only gives up when Rias holds him in her arms and surrenders.
- Did You Just Punch Out Cthulhu?: Issei's fight against Riser. He sacrifices his left arm in order to obtain some powers from his Sacred Gear. But more importantly, since it's no longer technically his arm, he is able to hold the cross and utilize holy water against the otherwise undefeatable Riser without the usual repercussion of a devil holding holy items and taking damage.
- Disney Death: The pre-credits scene of Episode 11 shows Koneko fading away in a shower of sparkles after being fatally wounded in an expolosion from Riser's queen during the rating game in the climax of the previous episode. Rias quickly explains soon after that she's just been sent to a holding area until the game ends.
- The Dog Bites Back: After Issei and his allies are beaten up by Riser and his harem, Issei decides to fight Riser and take Rias back for good.
- Earn Your Happy Ending: After going through a Rating Game and an Engagement Challenge against Riser Phenex and his peerage, Issei finally gets Rias as his first girlfriend.
- Engagement Challenge: Issei challenges Riser to a battle over his engagement to Rias, and ends up winning, freeing Rias from the loveless marriage.
- Facial Horror: Riser's face gets burned by Holy Water in the volume's finale.
- A Father to His Men: Rias forfeits the Rating Game when she realizes Issei will not stop trying to defeat Riser, no matter how much Riser hits him.
- First Kiss: Rias gives hers to Issei in the climax.
- From Bad to Worse: Riser turns up and Rias proposes to hold a Rating Game. Then the Occult Research Club gets defeated by Riser's allies. Then Riser brutally attacks Issei. Then Rias is forced to stop the game by resigning before Issei gets injured any further. And this happens a few chapters before the Engagement Challenge between Issei and Riser.
- Girl with Psycho Weapon: Several members of Riser's Peerage use chainsaws and swords.
- Grand Finale: For the first story arc, setting in motion the "Birth of the Breast Dragon Emperor" arc.
- Mass "Oh, Crap!": Koneko, Xuelan, Mira, Ile and Nel have a moment of terror when Issei is about to use Dress Break for the first time.
- Moment Killer: When Rias enters Issei's house to break off her engagement to Rias, she tries to have him take her virginity. Unfortunately for them, Grayfia shows up just as they are about to do the deed.
- Oh, Crap!:
- Issei when Mira rams him into the gymnasium's wall during the Rating Game.
- Xuelan when she's finally defeated by Koneko.
- Mira, Ile and Nel when Issei activates Dress Break.
- Riser when Issei burns his face with Holy Water and when he is about to deliver the final blow.
- Ravel after Issei beats Riser into submission.
- Punch! Punch! Punch! Uh Oh...: Xuelan tries to kick Koneko, with virtually no effect, who then punches her and gives her a Curb-Stomp Battle.
- Shut Up, Hannibal!: At the end of the volume, Riser tells Issei that his engagement with Rias benefits the future of all devils and that Issei has no business in interfering with it. Issei punches him out in response.
- Villainous Breakdown: After Issei continues to interfere in his plans, Riser eventually loses all sense of gentlemanly restraint he'd shown throughout the volume, even resorting to enraged snarling when his face gets burned by Issei's Boosted Gear Gift.
