Just says after Rainbooms manages to destroy the memory stone and restores their memories back, Sunset was about to approached Wallflower when Speed (who is immune to the memory stone thank to Kyan's powers) beat her to it and he have the most pissed off face with bloodshot eyes.

Speed: (angrily) So you willing to put Sunset through HELL AND THREATENING TO ERASE MEMORIES OF MY RAINBOW DASH!!!!! AND SUNSET'S FRIENDS ALL BECAUSE THEY IGNORES YOU?!?! UNFORGIVABLE!!!!

(Yes, Main Rainbow Dash would accompany with him and she probably dealing with her human counterpart who have her memories of Sunset taking by Wallflower… in other words, there's two Rainbow Dash in this scenario)

Wallflower: WAIT, I CAN-

But it was too late as he summoned a giant dark red aura around him as his body starting to transform into more darker, more sinister-looking and his mouth covered up to make him more like an evil-looking demon as he surrounded by bats

His father is there as he gasped at the sight.

Axel: Wallflower! What have you done?!?!

Red Shot grabs her before throwing her to the school's wall and gives her a No Holds-Barred Beatdown like what Omni Man did to his son before he stops as Wallflower's face is all messed up and bloodied before summoned a swarm of bats to eat her body.

(Skipped to 1:33)

Axel would throw a formula to your OC.

Axel: OC!!! You must inject him with the formula! That will change him back to his old self! He isn't being himself right now! He thought Wallflower was going to hurt Rainbow Dash and he let Red Shot come out!

He would explains to your OC and Rainbooms including Speed's Rainbow that anyone who born with "Red Shot" condition would transform into Red Shots when their loved one are either get hurt or thought to be killed and unfortunately, Wallflower learned that the hard way.

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Axel: Star Wing!!! You must inject him with the formula!

"Got it," Star said, speeding forward and injecting Red Shot with the formula. She put herself between him and Wallflower as the formula took effect.

"Alright, big guy," Star said. "She's had enough. As much as I hate the idea of forgetting things too, I think you more than made it clear why she shouldn't do that."

Rainbow Dash would also get between him and Star.

"Look at me, Speed," she said firmly. "I'm fine, not a scratch on me. And I still remember you, my friends, Sunset... everything! There's no reason for you to be bringing out that crazy Red Shot thing. Tone it back, okay? All eyes on me. Deep breaths. Come back to us, Speed."

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"Look at me, Speed," she said firmly. "I'm fine, not a scratch on me. And I still remember you, my friends, Sunset... everything! There's no reason for you to be bringing out that crazy Red Shot thing. Tone it back, okay? All eyes on me. Deep breaths. Come back to us, Speed."

He take deep breaths as he turn back to normal before looking at beaten and bloodied Wallflower and then Rainbow Dash before hugging his girlfriend

Speed: I'm so sorry, Rainbow!

Axel walk toward Wallflower and uses his Zeronos to undo all injuries Red Shot inflicted on her and she's fully healed while he gives her a disappointment look.

Axel: Ms. Blush, I understand you didn't have great time with Sunset but erasing memories of her friend's time with her and then erasing their entire memories out of spite? That's going way too far especially when your reason are rather petty… I won't tell your parents about memory stone but I will tell them how much you caused trouble for Sunset and her friends and my boy.

He then gives her a sad look

Axel: Wallflower, powers like Memory Stone are very dangerous and can bring consequences to yourself as I learned the hard way when I contain my sword… everytime I used my sword, my lovers' memories of their time with me will be erased and it's very painful to deal with! So don't ever made same mistakes as I did… and don't blame my son… the only person you should blame on is yourself… you brought this on yourself.

He look at Rainbooms.

Axel: Don't be scared of my boy, he have a condition he couldn't control and that's why I am working on finding cure for him, so don't hate him for what he did to Wallflower… he was scared that Rainbow won't remember him if Wallflower steal her memories…

He then walk toward Star and Rainbows before giving them formulas

Axel: Made sure to inject my boy with those formula so he wouldn't let himself to transform into Red Shot again, alright?

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Axel: Don't be scared of my boy, he have a condition he couldn't control and that's why I am working on finding cure for him, so don't hate him for what he did to Wallflower… he was scared that Rainbow won't remember him if Wallflower steal her memories…

I imagine the Rainboom Rainbow would be glancing at Speed and her Pony counterpart, suddenly very nervous since she likely doesn't have memories of him, and thus is worried that pointing that out would bring back the Red Shot persona.

"Well," she'd note. "Good thing I... or... Rainbow... remembers him, right?" She chuckled nervously. "Please tell me that formula's not bringing that Red Shot guy back..."

He then walk toward Star and Rainbows before giving them formulas

Axel: Made sure to inject my boy with those formula so he wouldn't let himself to transform into Red Shot again, alright?

"You got it," Star replied, placing the formulas somewhere Rainbow and herself can access them easily. "The minute he starts seeing Red, Rainbow, we act."

Rainbow nodded, before a voice piped up.

"So..." Red would note from the treeline. "Should I stay out of sight then?"

Star scoffed. "Not what I meant, Red, you're fine."

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"Well," she'd note. "Good thing I... or... Rainbow... remembers him, right?" She chuckled nervously. "Please tell me that formula's not bringing that Red Shot guy back..."

Axel: (nodded) I'm promise that formula will hold him down.

After Axel telling Wallflower's parent about her actions which got her grounded for 3 weeks... Speed and his Rainbow back to their home as Speed look at his beloved marefriend.

Speed: (sighed) Rainbow, I'm going to be honest with you... when Wallflower admits her reason of hurting Sunset, I got very angry cause she reminds me of my old self and I hate that... looking at Wallflower is like looking at myself and I don't want to go back to that person... if she had steal your memories, I would just be like a nobody and I definitely don't want to be a nobody.

He hold Rainbow's hoof and tighten his grip on her but not too hard.

Speed: I don't know what to do if she steal your memories... I'm scared, Rainbow... I thought you wouldn't remember me if your memories were taking by her.

[Insert Rainbow's response]

Awesome work!

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Speed: I don't know what to do if she steal your memories... I'm scared, Rainbow... I thought you wouldn't remember me if your memories were taking by her.

[Insert Rainbow's response]

Rainbow Dash chuckled. "Come on, Speed; you're too awesome to be forgettable. You're funny, you're noble, you're adorable... there's no way you could be a nobody now." She'd kiss him. "I promise; no one's taking my memories of you. Ever."

Rainbow Dash might be showing some overconfidence, but she is hoping to make Speed feel better, as she doesn't want to forget him. And, as mentioned, I believe she'd still be determined enough to have a shadow of a memory left behind, so even if Wallflower did erase her memories, she'd still recognize Speed from somewhere, and insist she knows him.

Always happy to share.