The Legend of Sol, Titan, and Morgan: Paladin

When Morgan returned to her siblings, Titan immediately saw a new happiness and a new warmth in her that could only mean one thing. He congratulated her roundly, then teased her cheerfully until Sol interrupted them, to ask if Morgan was going to allow her personal feelings to interfere with their quest.
Morgan forced herself to be as respectful as she could in reply, and yet at the same time, she felt like a chasm had just been cut between her and her sister. As much as she loved her, adored her, respected her, all the same they were very different ponies, after all. Morgan was a creature of passion, and action, and who worked best in the darkness, striking with the ferocity and the directness of a dragon. Sol, meanwhile, was the Sun-Blessed, the Dawnbringer, and a pony who acted coldly and logically, pushing her emotions aside.
And even when Sol gave in to her emotions and Morgan repressed her own, they acted as opposites: in rage, Sol would kill, terrify, demolish, and burn enemy and friend alike to satisfy her bloodlust or need for revenge. But Morgan would act with honor even at her coldest, refusing to harm the innocent, striking with precision instead of cruelty, always putting others above her own well being.
Sol plainly did not like this relationship, nor where it was heading: yet all the same, she grudgingly accepted Morgan's word and said that she would not interfere. Morgan was placated by this, and Titan smiled, hoping it was an honest sign of improvement in their wise and yet stunted sister, and yet at the same time worried that her words were hollow, and she was instead already planning ways to take advantage of Morgan's affiliation with a Templar of the Order.
But for now, Sol had decided to simply watch and wait: part of her was still honestly surprised to discover that Morgan had decided to take on a partner, and moreover, one who was so young, but struck her as fragile and foolish. Mortal lives, after all, were short: shorter still when cowards tried to pick up swords in an attempt to act like brave stallions.
Perhaps it was cruel of her, but Sol thought that Morgan was going through a defiant phase, or perhaps longed to join the normal lives of these mortal ponies around them, who they were all striving to protect. Perhaps she had romanticized them, or perhaps this was even similar to how a foal would want to adopt some little bird or fish or rat, not realizing how fragile and short-lived they were, giving it love and affection only to shortly experience its loss. But sometimes from that experience, a foal could learn about letting go, or to harden their heart against loving such fragile and weak things: Sol hoped that Morgan would learn the latter.
For mortal ponies were weak, and short-lived, and not worth their time and affection. She believed wholeheartedly that the ponies could unify, build a mighty nation, and she would protect that... but what she loved most about these ponies was their ideals, and not the ponies themselves. She would discard a hundred, a thousand, a thousand more of these ponies if it meant it would help inspire Equestria into falling into the step she wanted it to; if it would help these ponies understand how weak and vulnerable they were, and that they needed their protection, leadership, and guidance.
She only hoped that Morgan hadn't started to foolishly care about these expendable servants to her plan for the greater good.

The Legend of Sol, Titan, and Morgan: Fate's Fools

For a time, Sol, Titan and Morgan went back to their lives in Canterlot: while they were ever-vigilant for any attack or threat, Morgan and Titan found themselves relaxing, and even enjoying their time in the city. Sol refused to lower her guard, saying that there were threats both within and without, but Titan soon felt a whisper from nature that told him this wicked goddess had met her own troubles, and Morgan said she saw signs in the stars that something dangerous had been awoken to the north... and it most certainly was not some false goddess.

Sol found herself concerned that there would soon be another foe threatening them, but Titan and Morgan thought that if their enemy had made an enemy of something else, it was all the better for them, and all the more reason for them to take this time to relax and put their efforts towards other things. So Titan worked the forge, and spent time both at the bar and on the training field with the soldiers they had recruited, getting to know each and every one of them by name, learning about them and making friends with them.

Morgan, meanwhile, soon grew bored: she took to taking her fun at the Baron's expense by meddling with his trade caravans and his guards, and making other challenges. Sometimes she would be caught, and punished by the Baron until Sol came to her aid to free her from the dungeons. Other times, she would have to escape herself from the guard, or whatever imprisonment she was placed in, be it a cell or the stocks.

Sol would scold Morgan after each of these little events, and Morgan took most of these in stride: but finally, when Morgan had made sport of an important trade caravan and damaged goods destined for the magic academy Sol had hoped to make use of herself, the eldest sibling had punished Morgan like a child, taking away all her weapons and armor and sending her out into the street for the night.

Morgan was able to find little solace in Canterlot: even if her magic could insulate her against the cold of the night, she all the same felt a chill that magic alone could not keep away. The ponies of the city treated her uneasily, for she was known to use dark and dangerous magic as well as for her constant testing of the barony's laws, and the guards were all too eager to run her out of any place she tried to den, or for any excuse to try and fight her or mock her. And Morgan, for all her anger and pride, was also afraid not of Sol's wrath, but of being a greater disappointment to her sister than she felt she had been already; so each time the guards came after her, she was forced to flee and take wing, and each time felt like it added a splinter to her soul.

Eventually, Morgan found herself forced to flee into the holy grounds where the Templars had set up their order: she hid there, knowing the guards wouldn't enter, but at the same time afraid that the Templars would find her and throw her out. 

But to her surprise, when she was found, it was by the young stallion who had seemed so taken with her: he invited her in as his guest, bringing her not to the dormitories or the church, but the building where the captains and the administrators kept their offices and stored the treasures and valuables they had taken over the course of their many successful campaigns. They walked together through the great marble halls and studied the paintings and admired the weapons and busts of old heroes left on display, neither speaking much, but only enjoying the beauty and silence of the empty halls.

They were almost caught by a patrol, but in a flash, Morgan pulled the young knight aside and drew him into another room, then used her magic to conceal them both. They pressed together as the templars passed... and didn't pull apart until long after the patrol had wended on its way. And when they finally did, the young knight tried to steal a kiss, but hesitated too long, and his lips merely brushed the cheek of the mare chastely.

Yet because of his hesitance, his innocence, Morgan found herself drawn to him: she teased him, and then led him out into the halls, filled with warmth and happiness and feelings like she had never had before, for any stallion. In the past, oh certainly, she had adored and enjoyed the company of others, but never had she felt this bubbling euphoria, this unexpected joy.

They ran through the corridors until they ended up at one of the vaults, and there, Morgan challenged the young knight to open it. He was afraid, and hesitant, but all the same he wanted to impress her, so he tried his best to: but he was fumbling and clumsy and soon set off an alarm that rang through the whole building.

He panicked, but Morgan only laughed before sweeping him up, and he was amazed as she used her magic to simply whisk them both away, out of the temple, out of the templar's holy grounds, out of Canterlot itself and into the mountain wilderness.

He was young and innocent and a fool, and she knew then that she loved him for those things: she kissed him without hesitation, and he kissed her back, and there beneath the stars they joined in love. There, beneath the stars, they shared themselves with one-another... and Morgan didn't care that in the future, she knew that time and duty might draw them apart. For now, all she cared about was that she had someone to call her own, and to love as she had never loved anyone before.

The Legend of Sol, Titan, and Morgan: A Victory Better Left Lost

When Sol, Titan, and Morgan returned to Canterlot, they received praise and adulation from the cityfolk as word spread of their deeds, and that the monsters that had plagued the highways and mountain passes had been defeated and driven off.
But very soon, they were called to the castle, and there they did not receive praise but instead cold looks and anger. Morgan and Titan were both confused, but Sol was unsurprised. It was clear that the Baron had disagreed with her decision, which didn't surprise her.
The Baron met with them, and cursed them for fools: he said they would bring the anger of the goddess down on them. Swiftly, before her brother or sister's emotions could get in the way, Sol asked how the Baron could possibly know of the goddess Veliuona, before she also questioned if he had really thought they were going to just walk away... or let themselves die at the claws of the undead.
The Baron was surprised by all this, but he took only a moment to gather his thoughts before he grudgingly admitted that yes, he had known that the Lich was not the true source of the evil. But it was not because of any alliance or meeting with Veliuona herself: rather, she had been slowly but steadily expanding her powers through the swampy territories to the far west, and it was said that at least one barony of Equestria had already fallen to her powers. Canterlot was mighty, but they were in no shape to do battle with an undead goddess and her army of evil.
He had not expected them to fail, nor sent them into ambush: Sol believed this. The Lich had been far too proud of herself for figuring out Sol's identity and had revealed far too much to them for the Baron to have warned her of precisely what she was faced with.
But he had also not expected that Sol would not order a retreat, and nor would she try to palaver, but instead destroy the Lich. And his mood was worsened still more when Sol said calmly that she had actually used the Lich to send a message: she would return to her master and likely be reconstituted.
The Baron asked incredulously what the point of such a brash action was, but Sol countered that it wasn't brash: they were sending a message, and making it clear that they were not afraid of her. She was also certain that Veliuona would not take action against them immediately: instead, she would want to send a messenger, to give a display of power and pride. And Sol would gladly follow this messenger back to its source, to meet the goddess herself.
The implications were clear from her statement: Morgan looked excited, and Titan looked thoughtful, but seemed to hesitate ever so slightly, worried for what unfortunate innocents could be caught in the crossfire, or if Sol was wrong. But Sol projected confidence and strength... enough that the Baron finally grudgingly said he would allow them to continue to use Canterlot as a base of operations, and he would support them however he could until the day that Veliuona contacted him.
He only hoped that Sol was right... and Sol could only hope herself that everything was going to go according to plan, no matter how much confidence she pretended to have.

The Legend of Sol, Titan, and Morgan: The Threat

Sol had a plan, and it was one that worried her siblings. Yet all the same, they trusted in her strategy, even if they both feared that the cost might be high. But Sol knew this was the easiest way to their foe, and the fastest, sharpest way to achieve victory over her, whoever and whatever she was.
Sol picked twenty of the Baron's soldiers, while Morgan and Titan modified shackles and manacles and chains: these were placed upon the uneasy ponies, who would play the role of prisoners until the time was right. Next, these soldiers were loaded into two carriages to be pulled by Morgan and Titan, while Sol took the lead, covering her armor and body with a heavy cloak. She could do little to hide her size, but her face and mane she concealed with a cloth mask and veil.
Once everyone was ready, Sol led them to the meeting place that the Baron had indicated, and found one of the strange undead they had encountered on the road waiting for her there. She noticed that this skeleton was slightly different, however: not only was it a unicorn, it had gemstones grafted to its rune-covered bones: perhaps to enhance its power, perhaps as marks of status.
It demanded to inspect the cargo, and Sol agreed, neither bowing nor resisting. She was unsurprised when other skeletons emerged from where they'd hidden themselves, while this lead creature came up to her, studying her intently.
But it made no move to unmask her: and once its minions were done counting the soldiers, the creature stepped away and told her to follow. So Sol followed, undaunted, knowing that they were headed into a trap, but determined to spring her own before her foes could take the advantage.
They were led to the remains of an old temple, where more skeletons awaited them. None of these held much interest for Sol, however: they were nothing but pawns and soldiers of a greater evil. And soon enough, the ruler of this black citadel made itself known: a Lich, a sorceress of vile and terrible powers who had used her magic to give herself an eternal unlife.
She greeted them cordially, and introduced herself as the commander of these undead, which she called 'Velites.' Sol studied her, fearless: she paid little heed to the threats and mockery of the Lich as the hordes of undead moved in around them. Instead, she analyzed how the Lich acted and spoke, and she quickly came to realize that while this Lich was a powerful enemy, she was not the true threat, or the leader of these Velites. Instead, she was likely a lieutenant of some greater evil.
Having learned what she came here for, Sol didn't hesitate to interrupt the Lich with a powerful spell, beginning a sudden and ferocious battle. Both Titan and Morgan leapt immediately into the fray, while the soldiers quickly broke free of their restraints: the manacles and chains had been modified in such a way that they snapped easily apart when pulled in the right direction, and left the soldiers with makeshift whips of chain and weighted bracers around their limbs. These iron implements were crude, but served well against the Velites, smashing their brittle bones with ease.
The Lich was powerful, but no match for Sol alone: with the strength of Titan and Morgan's fearlessness added to the raw magic of Sol, they made short work of the sorceress. She was left broken and beaten, but even as the last of her soldiers were destroyed or driven away, she was fearless: her evil spirit would return to her mistress in death, the Goddess of Cursed Shades, Veliuona
But Sol was unsurprised and undaunted, and she only gave the Lich a message for her mistress: that she would come for this self-proclaimed goddess and destroy her. And then, ruthless and merciless, she crushed the life out of the Lich with one hoof before checking on her soldiers.
Only a few had been killed: all-in-all, she considered it a great success. Morgan and Titan both seemed uncertain of Sol's actions, but all the same, they knew that the best they could do was trust in their sister and her plans for the future, and do what they could to conserve the lives of any unfortunate ponies caught in path of their sister's plans to destroy this unknown evil.