Knowledge filled Twilight's mind.
As the Elements strengthened the bonds of magic between her and her friends, the understanding of how to use the artifacts flowed into her in addition to the emotions of her friends.
It took a moment to sort through the maelstrom through her own mind, but eventually Twilight was able to pluck out what she needed first. A wave of prismatic energy shot out from her crown, impacting against a barrier that Discord had conjured up at the last moment.
He snarled at her as he pushed back against Twilight's assault, but her friends fed their own power through the shared connection and it was trivial to overwhelm his powers.
But, just as Twilight was about to channel her righteous anger into a final blow to wipe Discord off the face of the Earth, she saw the fear in his eyes, and faltered. The familiar guilt flared within her heart despite her best efforts, and instead of pushing through, she spread the Harmony magic around, allowing it to pulse out into the world and return all of it back to normal.
Reality reasserted itself as the rest of the local geometry became three-dimensional and analytic once again. The animals stopped speaking in tongues, and the plants were once again stationary. Incantation also reappeared in a puff of magic. "Aww," she whined. "I was just filling up!"
"Wait, where'd Lightning, Fiddle, and Marble go?" Rainbow asked.
"Well, while we were trapped in the Infinite Void, Lightning and Fiddle started making out to pass the time," Ink explained. "And then Marble finally got the courage to ask if she could join in, so they'll be with us when they're done with that." She pouted. "They kicked me out when you opened the portal, though."
Rarity sighed. "Well, luckily we won't have need of them." She turned to face Twilight. "Shall we end this once and for all, my darling dearest?"
Twilight swallowed the lump in her throat as she stared at Discord. She'd trapped him in a bubble of Harmony, preventing him from influencing the outside world with his powers. Time and time again, he snapped his claws, summoning increasingly large and comical explosions and weapons to try to hack, slash, stab, explode, and exfoliate his way out, but the spell held strong and kept him contained.
"Do it, then!" Discord shouted. "Finish what you started, Princess Sparklebutt, and kill your old friend. I'm dead to you anyways."
He was wrong. With Rarity's help, Twilight had forgiven herself for what she had done after Discord cursed her, and had accepted that she wasn't responsible for the Spirit's actions. But... that didn't mean she hadn't betrayed someone she genuinely had thought of as a friend, and who had thought of her as a friend in turn.
None of that justified what Discord had done, but did Twilight really have the right to pass judgement now?
It would be so easy to wave her horn and end Discord's existence, or to trap him in a prison for all eternity, without any chance of escape. And yet, she couldn't bring herself to strike down someone she'd already hurt once before, no matter his sins.
A storm of emotion threatened to pull Twilight under, as her righteous wrath and protective instinct warred with the remnants of her guilt and desire to try to rebuild that charred bridge between them. Spike and Cadance stood to the side, looking expectantly at Twilight, having suffered just as much or more from this ordeal.
Twilight couldn't breathe, and moments stretched out into seconds as they floated in the air, Harmony itself swirling around them as it awaited Twilight's decision.
"Twilight?" Rarity's voice brought the princess back into the present. "Is everything quite alright?"
"I..." Shame filled Twilight's heart. "I'm sorry," she whispered, and she didn't know whom she was talking to: herself, Rarity, or Discord.
Discord was the first to respond, however. "Oh, spare me your trite sentimentality." He snapped his claws and summoned up a tiny violin, along with a smaller version of himself to play it. "I'd rather be dead than listen to more of your self-pity."
"Shut up!" Rarity snapped. She took a breath to calm herself before facing Twilight. "Could we speak in private, please?" she asked.
Twilight nodded mutely, conjuring a bubble of silence around them.
"Thank you, dear." Rarity smiled gently. "Now, what seems to be the problem, Twilight?"
"I can't kill him," Twilight said, looking away. She couldn't face Rarity right now. "And I can't trap him like he did to me. I can't."
"Oh, my darling heart." There was no pity in Rarity's voice, only understanding. "Of course you can't. You're too good a mare to stoop to his level. But something must be done about him."
"Part of me still wants to try to save him," Twilight admitted, turning back to face Rarity. The unconditional love in her eyes gave her the strength to keep talking. "To try to bring out the good I know is still in him, like I should have done the first time. I'm much better at friendship now, and I think, with enough time, I might be able to salvage things."
"If that's what you want to do, then you have my support," Rarity said. "I trust you."
"I know, but that doesn't help me come to a conclusion," Twilight replied.
"Do you truly believe he can be reformed?" Rarity asked?
"I don't know. I think so, maybe?." Twilight sighed. "But, I'm not sure I could do it, not anymore."
"And somepony else could?" Rarity glanced around, where their friends were looking at them with worried eyes. Twilight could feel the concern and love they held for her through the bond of the Elements, and it warmed her heart.
"You're right." Twilight didn't have to do this alone now. That was the most important lesson she had learned.
Closing her eyes, she reached out to the other bearers, sending out a silent plea for advice.
Rainbow Dash was the first to respond, of course. Her fierce loyalty manifested itself as a desire to protect her friends, and her answer was clear; Discord could not be allowed to hurt any of them ever again.
The second of her friends to reply was Applejack, who fought through her anger to give an honest evaluation of the situation, which was the same as Dash's. Pinkie Pie wanted to make sure that Luna's laughter was never taken away again, but despite her grim pronouncement, she made sure to inject some of her own natural good cheer into Twilight, to remind her that her friends would support her no matter what she decided.
Of course, Rarity, in her eternal generosity, was willing to put aside her own vendetta if it would give Twilight closure. But she would only do it for Twilight, not for Discord, who could rot in Tartarus as far as she was concerned for what he had done to her beloved princess.
And then, just as Twilight thought she might might abstain, Fluttershy's kindness pulsed through their bond. She acknowledged the pain that Twilight had been through, and her right to never want to see Discord again, but she also reminded Twilight of her conviction that there was good inside of everyone. Though, bringing out that good was not Twilight's responsibility, and it didn't make her a bad pony for not wanting to try.
Through all of it, though, Twilight understood that her friends would support her no matter what she decided. And their friendship would survive this trial, they all are sure of that.
With all of her friends' input, she made her choice, and prepared herself to live with it.
"Goodbye, Discord," Twilight said as she ripped open a portal between realities and launched him through it.
"Wait, don't I get a final monol— aaaaaah!"
And then it was over.
With one final spark of Harmony, Twilight cleansed the rest of the courtyard of Discord's influence before allowing the Element's powers to return to their owners. For a moment, she felt empty, untethered from the world, and nearly collapsed onto the ground.
Rarity caught her, and soon enough her other friends were all surrounding them. "Darling, are you alright?" the love of Twilight's life asked her.
Twilight nodded. "I... I couldn't forgive him, in the end," she said softly. "But that didn't mean I couldn't give him a second chance, whether or not he deserves it. I sent him to another world, similar to ours but different, where another version of me might be able to make friends with him like I wanted to." A grim frown graced her muzzle. "And if that doesn't work, that world has the Elements too."
"So does that mean it's over?" Rainbow Dash asked, flitting above them impatiently.
Twilight nodded again. "Yes," she said. "It's finally over."