(Earlier after Akeno started fighting Yubelluna.)

Rias, Asia, Koneko, Mash, Mephy, Bunyan, and Altera were moving towards Riser's base where Berserker was causing havoc after Akeno went to confront Riser's queen. As they were making their way to the student council building Rias couldn't help but feel some anxiety. It's almost time to finish this. Can I really come out on top over Riser? No! I can't think like that! Issei and the others put in so much effort for me to get this chance. I can't betray that trust by doubting myself now. Rias put on a stern face. We will win and then I will confess to Issei how I feel. There won't be anything to hold us back then. Rias thought to herself.

As they were approaching they were starting to hear the sounds of battle up ahead of them. Various explosions and crashing sounds were being made in front of them. As they got to the edge of the clearing they saw the battle. Berserker was taking on Riser and three of his peerage at the same time. Riser was launching large balls of fire while his servants were switching between supporting magic and engaging in CQC to try and distract her from Riser. "I will commend you for lasting so long against me and my servants, but there is nothing you can do to harm me. I will wear you down eventually so you might as well give up now!" Riser boasted.

Berserker just scoffed at Riser. "Hmph! You talk a big game but all you've done is give me some cardio and target practice. This barely even qualifies as a warm-up for me."

Riser gave her a smug look. "I can at least commend the Sekiryuutei for having such strong subordinates. Why don't you renounce him and come and serve me instead? I will treat you better as one of my women."

Rias and her group froze in fear once those words left Riser's mouth. They remembered how angry Berserker got when Issei just hinted at that topic. They weren't sure how things would turn out now that Riser actually said it. Berserker stopped moving for a moment making Riser think she was considering it. Suddenly a murderous aura erupted from her causing shockwaves around the immediate area. Everyone had to shield themselves from Berserker's fury. Her eyes were red with rage just like when Issei spoke with her and the ground cracked beneath her. Fear was etched on Riser's peerage's faces at the raw magic power they were feeling. Moments later Berserker's power calmed down and she showed a fierce smile. "It's a good thing my Master warned me of you beforehand. If he hadn't I wouldn't be able to hold myself back from tearing you apart." She said viciously. She then looked behind her. "But it isn't my place to defeat you. That honor belongs to her."

As if on que Rias and her group emerged from the woods. Riser saw her and regained his smug grin. "Rias. So you've finally arrived. It's good that you've come to me to face your defeat rather than making me come to you. You should surrender since there is no way for you to beat me. There is no point in dragging this out." He said confidently.

Rias was becoming irritated as Riser spoke but kept herself calm. If I let him get under my skin I might make a mistake and waste this whole opportunity. She thought. She readjusted herself and gave off a confident air as she spoke. "Surrender? You have yet to defeat anyone on my team and even though you can regenerate all we have to do is make you unable to fight. There are plenty of ways to do that." She said with a smile.

"Fine. I tried to make this easy but it seems you need to learn your place. So we will do this the painful way." Riser said with confidence. Riser's servants charged at Rias' group but were intercepted by the others. As they distracted the servants Rias, Mash, and Asia were left to face off against Riser.

Rias stepped forward while addressing Mash and Asia. "Mash, protect Asia. I will face Riser." She said determined.

Riser just laughed at Rias' actions. "You're coming at me alone? You're even more foolish than I thought." He created a large fireball and launched it at Rias. Rias took off to avoid it and responded with a blast of destruction. Riser moved to avoid it but was slow and got hit in the side. But a few moments later it was healed as if nothing had happened.

I expected that but it's still grading to see him so lazily avoid my attacks. He clearly isn't even trying to take this seriously! Rias thought to herself, annoyed. The two kings continued to exchange attacks and neither were making much headway. Riser avoided any serious damage and what little he did take was regenerated. Rias on the other hand had been doing an excellent job of dodging Riser's attacks thanks to her training against actual opponents and boosting her stamina over the trip.

Riser was starting to become annoyed. "You can keep dodging all you want but you will eventually tire out. Just surrender already! There is nothing you can do to-"

"Riser's knight retired."

He was interrupted by an announcement of one of his pieces being eliminated. Riser showed an annoyed expression while Rias' became smug. "Things just don't seem to be going your way Riser." Rias mocked.

"It doesn't matter how many you take out as long as I-"

"Riser's knight retired."

Riser was once again interrupted by an announcement of one of his peerage being eliminated. Rias was holding in her laughter at Riser being made a fool of again. If Issei planned this he is a freaking genius. I doubt it though. She thought to herself. "I'm sorry. What were you saying again?" She teased mockingly.

Riser had moved from annoyed to angry. "Why you! How dare you try to make a fool of-"

"Riser's pawn retired."

Rias couldn't hold it in anymore. She began to laugh hard at Riser's misfortune, she felt her stress that had built up leave her. I really needed that. She thought.

Riser had had enough. Flames began to erupt from his body and he prepared a large fireball to launch at Rias. "I've had enough of this foolishness! I will defeat you here and now!" A giant flaming ball formed above Riser as he lifted his hand. Rias was trying to get her act together as this was happening. Before Riser could launch the attack.

"Riser's rook retired."

Riser was distracted by another announcement of his peerage being defeated, giving Rias time to prepare. However she wasn't fast enough and Riser launched it at her. Before the attack could hit though something bright intercepted it and collided with the attack causing an explosion.

KABOOOM!

A great shockwave was created from the attacks colliding and both Rias and Riser were pushed back. The servants and Riser's peerage who were fighting off to the side were pushed back as well and had to get their bearings. As Rias was reorienting herself several fireballs came towards her through the smoke. She managed to dodge them and prepared to fire back. The smoke finally cleared and Riser had a clear sight on Rias and started to spam fireballs. Rias was building up power while dodging Riser's attacks. Once she got it she moved in close to Riser and fired the blast. It moved towards him at great speed not giving him much time to dodge. The attack hit him directly and sent him crashing into the ground. After a bit Riser picked himself up off the ground and started regenerating from his wounds. Rias clicked her tongue in annoyance while Riser also looked back at her annoyed.

"Riser's queen retired."

Another announcement was made and this one actually made Riser make a shocked expression. "Impossible! No one on your team should be strong enough to defeat Yubelluna!"

Rias showed a pleased smile. "Looks like Akeno was able to deal with the Bomb Queen. That just shows how well our training went. I will tell you again, Riser. Don't underestimate me or my peerage." She stated proudly.

More flames started erupting from Riser as his temper was reaching its boiling point. "Don't get cocky brat! Despite your improved power it's still not enough to defeat me!" He launched a large fireball combined with wind magic to increase its speed at Rias which took her by surprise.

But before it could hit her Mash got between the two of them and blocked the attack. Rias was taken by surprise not expecting Mash to jump in. "Mash-san!? What are you doing!? What about Asia!? Rias asked, concerned.

"Don't worry, she is covered." Mash stated. Rias looked over to Asia and saw the others standing by her, some of them getting patched up by Asia. Then she looked over to where Riser's other servants were and they were on the ground fading away.

"Riser's two pawns and bishop retired."

Rias smiled and looked back towards Riser. "And now you are all alone. I think it's only fair that I give you the same offer you gave me. Surrender Riser."

Riser had now reached his boiling point. "Surrender!? ME!? Don't get ahead of yourself! I've never lost and I won't have my first loss be to a brat like you!" He launched himself at Rias and Mash gathering flames in his hand and kicking up strong winds.

Mash went to meet Riser head on blocking his attacks with her shield while Rias started firing magic from behind her. Riser couldn't get past Mash's shield and was getting more agitated every time he got hit by Rias' attack. After a bit of back and forth Riser got fed up and turned his attention to the observing group. "Fine! Since you're so confident because of who you have on your team then I will just get rid of them first!" He yelled and launched a large blast of flame at Asia and her group.

Everyone was taken by surprise and Berserker stood in front to cover Asia. Luckily she didn't have to. "Order Change!" Someone yelled and suddenly Mash and Berserker swapped places. Mash was disoriented for a second but quickly took a defensive stance and activated her skill (Honorable Wall of Snowflakes) to negate the damage for herself and everyone close to her.

The group was consumed by the flames and Riser showed a smug grin thinking he beat them. That look quickly changed to shock as everyone emerged from the flames unharmed. "Impossible! How did you get over there so quickly!? Not only that but you all came out of that attack unscathed!" As he was standing there yelling in shock he was suddenly met with a giant spiked ball and chain to his face. Berserker had swung her weapon at him, enraged at his dishonorable conduct.

"You trash! You're even worse than… that man. You call yourself a noble yet you don't have a shred of honor! I'll-" Berserker was yelling and about to lay into Riser when she was stopped.

"That's enough Berserker. I'll take it from here." Everyone turned to see Issei emerge from the forest followed by Kiba, Artoria, and Enkidu. Not long after, Akeno and her group also arrived from the air and landed next to the group.

"Issei-san!" Said Asia elated. She and the others walked up to the group and Asia and Medea Lily healed Issei back up.

After that Issei began walking towards Rias and turned to face Riser. "You look like you're having a tough time Fried Chicken. Didn't you say this was going to be an easy victory and that your peerage would wipe the floor with Rias'? Looks like you were all talk, like I expected."

"YOU! This is all your doing! If you didn't interfere this would have all been settled already!" Riser was screaming at Issei with waves of power flowing out of him and his face was regenerating from Berserker's attack.

Issei just gave him a smug look. "Hey, you were the one who agreed to the terms. Maybe if you had half a brain you would have thought this through. But it's too late to go back on it now. After all, I'm sure the Maoh would have something to say about your cowardice and inability to follow through when you're at a disadvantage. Plus, I don't think he will be too pleased with how you've been talking to Rias during this fight whether you win or lose."

Riser realized the truth in Issei's last statement. It was well known in the Underworld that Lucifer was basically a siscon so he wouldn't stand for Riser's behavior, agreement or not. Rias on the other hand noticed something about what Issei said. "Wait, if you knew Riser said that then that means you were here for a while."

Issei showed a slightly embarrassed look. "Well, I did arrive a bit ago but you were doing pretty good on your own and I didn't want to steal your thunder, so I stayed hidden and watched until he attacked the others." Rias slightly blushed at the compliment. Issei then turned to Berserker. "Berserker, go with the others. Rias and I will handle this." Berserker nodded and went with the others.

Riser finished regenerating and was now glaring at Issei and Rias. "I've had enough of you two causing me problems! It's time to end this facade!" He launched another flame blast at Issei and Rias. Issei stepped in front of Rias and created a magic barrier to block the attack. The attack hit the barrier and exploded, consuming the pair in flames. Riser started laughing. "Hahahahahaha! An easy victory!"

Rias' peerage looked worried while the servants just observed cooly. As the flames burned they suddenly began to swirl and rise into the air. Riser was confused as to what was happening. Suddenly a red light shown in the middle of the flaming tower.

[WELSH DRAGON! BALANCE BREAKER!]

A burst of power blew away the flaming tower and there stood Rias unharmed and Issei now clad in red draconic armor with green gems decorating its form. Everyone there had a look of surprise, even the servants. Issei stepped forward and took a stance. "I hope you're prepared Fried Chicken, cause the real fight starts now."

Issei launched himself at Riser at great speeds which caught Riser unprepared. He only managed to conjure flames in his hands and the two traded punches to the face. Issei's punch launched Riser back with great force, but Issei took some damage too as some blood was spit out of his helm. Riser had a smug look seeing that he hurt Issei and prepared to attack again when he was hit by destruction energy from Rias. He was distracted by Issei and didn't manage to dodge Rias' attack which significantly damaged him. As he was recovering Issei had launched himself at Riser again now with a red spear in hand and boosting power into himself. Riser tried to put some distance between himself and Issei but was met with a surprise attack from Issei who created magic runes and launched ice spears at him. The spears pierced Riser and damaged him further but quickly melted from his flames and the wounds were regenerating still. Because Riser had to regenerate he was beginning to slow down, which made him an easy target. Issei closed the gap and used the spear to wound him more then slam him into the ground.

Riser began to get back up when he was bombarded again with destruction energy and ice spears from Rias and Issei. Eventually he had enough and flames erupted from his whole body in a massive explosion. Issei moved to block Rias from the attack and both were hit by the attack. The pair were picking themselves off the floor from the attack. Issei took the brunt of the attack so his armor was broken and cracked in many places and eventually faded away all together. Rias was scuffed up and worn out herself. Riser finally fully healed and began walking towards the two. He wasn't even showing his usual smug look, he was supremely pissed. "It's time to finish this. You two have wasted enough of my time and all your efforts were for naught. Begone from my sight!" He prepared to finish them off but was suddenly stopped by chains that seemed to emerge from nowhere. Off to the side Enkidu created chains to bind Riser. Riser tried to move but the chains kept him in place. "You think chains can stop me!? I will just melt them with my flames!" Riser concentrated his flames and released them from his body, but the chains were unaffected.

Issei was picking himself up off the ground with Mash's help while Akeno helped Rias up. Asia and Medea came up to them and healed them a bit but Issei was preparing to end this now. "Mephy, Bunyan, it's time!"

"Y-yes Master!" Answered Bunyan.

"Now is when the fun begins. Hehehehehe." Replied Mephistopheles.

The two moved to opposite sides of Riser to enact the plan. Riser was still struggling to get free. "Grrrrrrrrr! Even chained don't think you can do as you please!" He tried to erupt flames from his body again to blow away his surroundings.

Issei wasn't going to let that happen. He reached out his hand towards Riser and activated his second Mystic Code. "Gandr!" With that Riser was stunned on top of being bound.

Riser was confused. "W-why!? Can't I!? Move!?" He could barely get the words out.

With that done Bunyan and Mephy used their skills (Popcorn Blizzard and Impotent Rage) on Riser, weakening him. Issei looked to Rias and spoke. "It's time to end this. Let's finish him Rias." Rias nodded and the pair stood side by side. The pair increased their power to launch a combined attack.

[BOOST BOOST BOOST BOOST BOOST BOOST BOOST BOOST BOOST!]

The pair combined Rias' destruction energy and Issei's Dragon Shot. "Eat this! Destruction Dragon Shot!" Issei stated and the pair launched their attack at the trapped Riser. The attack hit him dead on and caused a massive explosion. After the smoke cleared Riser stood in place still bound but he was clearly unconscious and severely wounded from the attack. Eventually his body started to glow and faded away.

"Riser has retired. The winner is Rias Gremory and her peerage!"

With that announcement everyone cheered. They were happy about their victory and proud of their progress. Issei fell on his back exhausted and Rias collapsed to her knees, tired as well. The two looked at each other and began to laugh. They were releasing their stress that was built up in their body during the fight. As they were celebrating someone came over to them.

"You really did it! You defeated my brother!"

It was Ravel who had been watching the fight from afar. Issei sat upright and gave the girl a wide smile. "See? Told you I could do it. Well, more like we did it but you get what I mean." He said nonchalantly. Ravel just looked at him, not sure what to say, so Issei kept speaking. "So, your family will honor the agreement, right?" He said while slightly narrowing his eyes.

Ravel got her act together to look and sound proper. "Yes we will. Especially since this battle was observed by the Maoh. The engagement is no more." She then turned over to Rias and bowed, which took the red head by surprise. "I'm sorry you had to go through all of this Ms. Rias. I didn't think anything of this situation until the Sekiryuutei explained to me how wrong this whole situation could go. On top of that, I would probably feel the same if I were in your position as well." She had a slightly sad look on her face.

Rias just shook her head. "You have nothing to apologize for. It's not like you could have done anything about it anyway. Now that it's done it's water under the bridge in terms of you and your family."

"Even my brother?"

"..."

"Yeah, I guess that would be too much to ask for."

As the two were talking Emiya finally arrived and with his arrival Grayfia appeared to take them back. Before they left, Issei went to Emiya and whispered to him. "Good job covering Rias earlier." Even though Issei was preoccupied with fighting earlier he could tell Emiya had done something, and not long after that the explosion was heard so he figured out it was his doing. Emiya just smirked slightly and everyone teleported away.

Ladies and gentlemen, we have a winner! Yeah so, I tried to make this as entertaining as possible while making it believable. It was kinda hard to do anything entertaining for Rias because all she has is long range attacks and even if she could do CQC Riser isn't the best opponent for that. I'm sure it's not surprising for those who got the hint during the training arc but Issei has balance breaker so he can do pretty good in a fight. This battle was about Rias Riser and Issei, so they were the ones doing the heavy lifting but naturally the servants helped to execute the plan. Now to address two questions in the comments. No, the other pantheons aren't watching this because we are not yet at the part of the story where the factions are coming together. Also, no, the ORC doesn't know Artoria is King Arthur and she is using invisible air on Excalibur, so Kiba doesn't notice it and thus doesn't freak out.