This battle's gonna take more than one part, much like how this story battle in-game is kinda long.
Chapter 23 – The Tower of Black Winds (Verdant Rain Moon)
An arrow whizzed by Byleth's head as she dodged to the side, allowing Bernadetta's shot to fly straight into the left eye of one of the thieves, putting him down instantly. The timid girl made a small gasp of surprise that she had scored a hit.
"Got him… I got him!" she shouted with uncharacteristic enthusiasm.
"Nice shot, Bern!" said Dorothea as she hid behind a broken pillar.
"Thanks, I – EEK!"
Bernadetta's self-praise was short-lived as a retaliatory arrow narrowly missed her leg, making her spring away from it in terror. Dorothea sighed at this; some things would never change, it seemed.
So far, the students had made considerable progress through Conand Tower. Many thieves had already succumbed to their efforts, with no casualties on the students' end. There was still a way to go, though, and Dorothea could hear the sound of many footsteps above them as they advanced. The bulk of the thieves were moving to meet them further ahead.
At the front of the students' column, Gilbert, Edelgard and Dedue held up their tall tower shields as they pushed the line forward. Arrows and javelins continually bounced off their sturdy defense. Whenever one of the thieves moved to try and attack at close range, they would be swiftly countered by one of the others. The whole class moved in tandem, advancing forward in a manner that the thieves couldn't hold back.
Then, as the class neared a collapsed opening in the side of the tower, Ingrid flew up to the opening on the back of her Pegasus, Celdia.
"Professor Eisner!" Ingrid shouted. "There's another group of thieves heading up the tower behind us! Looks like they were coming back from a raid!"
This put a damper on the students' spirits. If this reinforcing group was not dealt with, they were sure to be caught in a pincer attack.
Before Byleth could say anything, Catherine shouted, "I'll handle them!" Then, pointing to a group that included Caspar, Raphael, Ignatz, Ferdinand, Petra, and Mercedes, she ordered, "All of you, come with me!"
Giving affirmative nods, the group followed Catherine as she made her way back down the tower. Mercedes stopped for a moment, though, as Annette briefly gripped her arm.
"Be careful, Mercie," said Annette.
"Don't worry about me, Annie," Mercedes replied. "We'll be back before you know it."
Mercedes then took off after Catherine's group, leaving the rest to continue their march up the tower. Ingrid flew off as well to support the others from outside.
A minute later, however, Gilbert frowned as he said, "Something is not right."
"What do you mean?" asked Dedue.
"We should have met more resistance by now. It feels like…"
At that moment, Felix whipped around to a pair of nearby doors that led into one of the tower's storerooms. Immediately as he did, the doors burst open as a hidden group of four thieves attacked, right into the middle of the students' formation.
"AMBUSH!" Felix shouted, rushing to meet the lead thief with his blade.
The thief smirked as he ducked down, revealing an archer behind him with her bow drawn and aimed right at Felix.
Felix didn't even have time to react before the whip-like Sword of the Creator shot past him and pierced into the archer's clavicle. She screamed as she released her arrow, which still flew at Felix. The heir of Fraldarius hissed in pain as the arrow was embedded in his left shoulder, but he continued his attack, slashing his sword to cut through the first thief's stunned face.
"Why you…!" shouted another thief behind the first two as he raised his own crude blade.
This thief too was intercepted as a javelin thrown by Sylvain impaled him through the chest. Clenching his shoulder as he ripped out the arrow, Felix did not have to look back to know Sylvain was smirking at this. The fourth thief who sprung from the storeroom was met by Lorenz's lance to his stomach.
"A paltry attempt," Lorenz said pompously.
But then, a chorus of shouting dropped the smiles on Sylvain's and Lorenz's faces as they turned back to the hall the group had been advancing down. Gilbert and Dedue immediately turned in the direction of the shouts to see several dozens of thieves and rogues charging at them, a disorganized mob that threatened to run them all down through sheer weight of numbers.
"INCOMING!" shouted Leonie as she hastily drew her bow and fired an arrow at the approaching mob, wounding one of the thieves.
Dorothea went wide-eyed upon seeing the approaching mob. She hadn't expected there to be so many thieves, nor had she expected such a concentrated attack. Claude, Ashe and Bernadetta also fired their own arrows at the thieves, but this did nothing to slow them down.
"Dorothea, come on!" shouted Byleth as she quickly tugged on the diva's shoulder.
Though initially surprised, Dorothea quickly followed Byleth as the teacher sheathed the Sword of the Creator and began to channel her Mana. Dorothea had to remind herself that Byleth had been learning Anima magic from Hanneman, and so she began readying her own spell. To her sides, Annette and Lysithea also began preparing their own magic. But as she looked back at the mob, Dorothea knew their individual spells weren't going to cut it. They needed something more.
Before Dorothea could ask, Byleth said, "Channel your power to Lysithea, now!"
It clicked in for Dorothea what Byleth was intending. Combining the Mana of numerous spellcasters allowed for the unleashing of much more potent sorcery than could be achieved by any one spellcaster. And Lysithea was by far the best mage in their group; she would be able to wield the most devastating spells.
Dorothea turned to Lysithea and began to feed her Mana to the white-haired fifteen-year-old while Byleth and Annette did the same. As they did, Lysithea's pink eyes began to glow as a Crest manifested over her body, the Major Crest of Gloucester. She extended her hands forward, black magical energy crackling from her fingertips.
In an echoing voice, Lysithea shouted, "YOU'RE ALL IRRELEVANT!" as she released Hades Ω, the most powerful Dark spell known in Fódlan.
A spiraling pillar of black flame formed in front of Gilbert and Dedue and careened at the approaching mob, which began to skid to a halt as they saw their impending doom. The thieves spun around and began scrambling to escape the spell, but it approached far too rapidly. Screams and cries of agony replaced the shouts for battle as the whole mob was consumed by dark magic.
Lysithea panted loudly as Dorothea looked upon the results of the spell. Over half the thieves had been killed by the spell, with only a few crawling away from the carnage, and none were left able to stand. The sight was unnerving to the opera star.
Dorothea then looked back at Lysithea as she said, "That was… um…" She couldn't find the words to finish her statement.
Then, just as Lysithea looked like she was going to retort, she winced loudly in pain as her legs failed her and she fell backward right into Edelgard's arms. In concern, Dorothea rushed over and knelt next to Edelgard.
"Lysithea, are you okay?" Dorothea asked with concern.
Edelgard placed a hand to the young mage's forehead as the girl seemed to break out in a cold sweat. Dorothea realized the spell must have taken a lot out of her.
"She'll be alright," said Edelgard. "She just needs time to recover. Channeling that much Mana through her body is not without its risks."
Dorothea nodded at this. Though combining Mana was a good way to produce powerful spells, the one casting the spell had to shoulder most of the burden.
The diva turned back to the others. Dimitri and Leonie had taken it upon themselves to finish off the wounded thieves. She knew not to stop them; the thieves were probably going to die even if they did nothing. Killing them quickly would be a mercy.
"We'll hold here for a moment," said Byleth. "Tend to the wounded."
"We should keep moving," said Felix. "The remaining thieves aren't going to wait for us to–"
"We hold, Felix," Byleth interrupted sternly. "That's an order."
Felix was about to protest again when Sylvain swept in front of him and said, "Hey, Miklan's not going anywhere. Besides, that looks like it hurts."
Felix scowled as he held his still-bleeding shoulder. "I'll be fine," he hissed.
Dorothea took this moment to step up to the young swordsman and said, "I'll be the judge of that. Hold still."
Looking at Felix's shoulder, Dorothea channeled her magic. To Felix's surprise, green lights began to form around his shoulder, healing his wound.
"I thought you said you didn't know how to heal," Felix said to Dorothea.
"I've been learning," Dorothea replied. Finishing her work, she then said, "That's better."
"Alright then, let's get moving."
Felix readied his sword as he stepped away from Dorothea, who then stopped him with a loud "Ahem!" The swordsman turned around to see Dorothea glaring at him with her hands on her shapely hips.
"Aren't you forgetting something, Felix?" Dorothea said crossly.
After a moment of hesitation, Felix sighed loudly and said, "Thank you."
Coyly, Dorothea then said, "Mmhmm…? Thank you for…?"
"Don't push your luck, woman. Let's go."
Deciding she wouldn't get any more gratitude out of Felix, Dorothea allowed him to head to the front of the students' column alongside Edelgard and Dedue. Turning, she looked at Byleth as the teacher looked down at her pocket watch.
The singer strode up to Byleth as she asked, "Everything alright?"
Byleth did not answer but nodded affirmatively.
"Well, whenever you're ready," said Dorothea.
Byleth did her best not to sigh in relief as Dorothea went over to talk to Edelgard. Unknown to the singer, the ambush would have ended far worse for Felix had it not been for Sothis' power. Byleth was relieved that her strike had saved the boy from a premature death, but she still felt she could have done better in that circumstance.
"Do you always fret like this when things don't go your way?" asked Sothis. "The boy is alive and that is what matters most."
Byleth did not move or speak, but Sothis could read her thoughts.
"Slowly but surely, you learn the limitations of my power. Just because I grant you the ability to turn back the sands of time does not mean you can be careless with it. And I suspect you shall need it again when you find this Miklan."
With that, Sothis went silent. Byleth was a little relieved that she had chosen to be quiet. The green-haired girl liked to distract her at the worst times, and she didn't need such a distraction in the middle of a battle.
Dorothea's dynamic with Felix is going to be present again in the future, just to note. But no, there won't be any romance between them; Felix has Annette, after all.
Oh, and who here spots the subtle FE manga reference I made?