At the end of every training session or seminar the Professor would always say: "great job today". There was a time when Mercedes still believed her. She's never been too confident, but at least she knew she had a defined role and was making progress in her training. She could heal, and she could do it well; she learned to hit the bull's eye from twenty yards and she was even making amazing progress in her horseriding class. Just months ago her friends and peers would often tell her how much they appreciate her gentle touch and unwavering support, and how pleased they were to see her making great strides. Yes, back then Mercedes was a decent student. She didn't really know when exactly did this change; it was a gradual process. Her short-lived success was just a facade, a dam holding a violent river, but the river was working it's way under and around the obstacle, and slowly, but surely, the dam was giving way.
The name of this river was fear.
If there was one thing that Mercie never learned, it was to stay brave and stoic in the face of danger. She still kept as far back as she could. She was good with a bow, but there was no use to it since she rarely got in range of anything. She liked to think she was just cautious. The Professor would often note that a dead cleric is of no use to anyone, and Mercie held dearly to this idea. Each battle, she would stay in the back, surrounded by her batallion and guarded personally by one of her peers. She'd wait for the injured to come so she could help them.
But battles were getting worse, and her support was needed closer to the battle lines. And Mercie honestly tried to be there for everyone else. She just wasn't decisive enough. Every post-battle tactical analysis would inevitably conclude with something like "we would have broken through here faster, but Mercie lagged a bit" or a similar phrase, and every damn time Mercie would profusely apologize and blush and promise she'd be better next time. She was still a good healer, best one they had, and she prided herself on that. Perhaps it was after a couple of particularly difficult battles that she first started slacking in her independent training and studies... perhaps her mind lingered all too often on her faults and her weaknesses. She started falling behind, but she still thought she'd get there, eventually. Sure, the other mages in the Blue Lions House, Sylvain and Annette, were progressing faster, but it wasn't a competition. What little pride Mercie had was, however, injured, because she was older than anyone else. And a much more devout worshipper of Seiros, too. She'd never admit this to anyone, but in her mind this made her a little bit better than some.
She'd still spend more time praying than training, of course. This was something that the Professor seemed to have some issues with. Little came out of it, though.
Then Byleth started recruiting people. Some of them were more experienced than anyone in the House. Catherine with her fiery smile and devout faith seemed a good friend to Mercie at first; however, after the very first battle this swordmaiden criticized the blonde healer harder than the Professor ever dared. "People die because you are slow", Catherine roared, her voice shaking Mercie to the core. "Why aren't you still capable of casting Physic if you prefer to stay behind so much?"
So Mercie started trying harder... but it just wasn't working... and then, one day, Byleth, Dimitri and Catherine told her that there would be a small change in the active roster.
"You clearly need more time to yourself", Byleth said, glancing at Catherine. "It's okay. You'll get there. But the forces of the Church under my command are losing too many people, and we have to minimize losses. We need to make changes. You're going to spend some time in Garreg Mach, Mercedes, while we are trying out alternatives."
And, of course, she didn't argue.
The alternative in question turned out to be none but Linhardt von Hevring. The green-haired sleepyhead was lured away from the Black Eagles. Mercedes sincerely wished him the best. Others in her position would secretly hope for him to utterly fail, because that at least would prove that the problem wasn't Mercie, it was everyone else being way too reckless. But Linhardt, despite his soft nature and lazy antics, turned out to be capable in the areas she wasn't. This was the final nail in the coffin for Mercedes as from that day on she knew she would be sitting on the figurative bench for a good while. It was only up to her to improve in her training and in her approach to battle, but months went by and she barely progressed in anything she tried to do. She still sang in the choir regularly, but even that once wonderful pastime no longer brought her any joy. Something was missing, and she didn't know what it was. Mercedes became reclusive and started shying away from the rest of the House, afraid of facing them, talking to them, taking up their time. She felt like an imposter among them. Slow, fearful, soft Mercedes, who despite having years of experience on any of the other students in the House could never even hope to be on the same level.
There was, though, one thing she could do that no one else could. It was not particularly useful and she kept it secret. Mercedes could shrink herself.
She discovered the ability by accident and still didn't know where it come from. She spoke to Professor Hanneman a couple of times, trying to gently pry into the mysteries of her own Crest to see if perhaps that's where the ability came from, but the sharp Professor quickly became suspicious of her and she didn't want to reveal her newfound skill just yet. Was it magic? She wasn't sure either. All Mercedes knew was that she could will herself into shrinking down to a far more miniscule size. At first she could only go down to a couple feet tall, and that was strange and scary enough, but through secretive experimenting she managed to tune her ability to her own wishes. Still, the low limit seemed to lie around half an inch. Or at least that was as far down as she managed to get ever since she learned what she could do.
To her shame, she spent far more time on this than on her studies or her weapon mastery skills. Her stagnation continued and Mercie kept telling herself she'd turn it all around, but in truth she was losing hope for that. She could, however, shrink, and that was a unique thing that only she could do. Before then, she was the tallest woman among the Blue Lions; it was strange to now be able to see her friends far taller than she was. Not to mention the men...
And she did see them frequently, because there was a peculiar detail to Mercedes's ability: it was much easier and much less taxing to shrink herself around others than it was to do so in isolation. She started hiding in public places before sunrise - sometimes in the dining hall, sometimes in the training areas, sometimes in the library or the study areas - and dwindle away as soon as someone would enter. Then, to her unending shame, she'd stay there, watching other students practice either alone or with each other. She felt like she was spying on them, but at the same time it's not like she was actually doing anything wrong, was she? She was trying to learn from them while honing her newfound skill, and perhaps at one point she would be able to tell Byleth and the Professor would find a use for this amazing ability. Perhaps she'd even investigate if it can be used on others. Then they could send a shrunken infiltrator into the enemy lines to spoil their water supplies. Or they could even reduce the enemies themselves, so that those foul men and women opposing the Church would have no choice but to surrender. Mercedes giggled, imagining thieves and rebels waving tiny weapons at a giant Dimitri or Ingrid...
Yet there was another part to her escapades in her shrunken state, and it was simply that Mercedes craved the feeling. She loved staying there, tiny, in the corner, unseen and beneath anyone's notice, and watching her titanic classmates clash - either in a steel flourish or in a pulsing vortex of magical energy. When swordsmen danced around the wooden floor, blades flashing, she could feel the vibrations caused by their steps and taps. She saw them all in a different light at those times. They turned into legends, divine beings, giant yet graceful. She adored them this way, she couldn't take her eyes off them, and with every such day that she spent as a tiny observer, a deeper, more shameful desire started growing within her. The virtuous Mercedes couldn't help but think of what it would be like to be closer to them.
But she could not, would not, risk it, she wasn't ready to reveal what she learned to do, and it felt way too awkward to admit that she's been shrinking herself for a good while now. She started losing sleep over it, and would often spend those night hours reading and catching up on her faith studies, and then eyebags appeared under her eyes and she had to ask Annette for a masking balm so that Byleth wouldn't notice. It was then that Byleth - or, more likely, someone else, like Catherine or Ingrid - decided that Mercie needed to learn to work harder since she still wasn't making any progress. The apparent solution was to get Mercedes to take responsibility for a lot of space maintenance - she'd be tasked with cleaning the classroom after a seminar or preparing a training space every so often. It took more of her time, but she didn't mind, because such occasions often gave her an opportunity to shrink herself once again. And watch. Bask in someone else's giant glory.
Nothing lasts forever. And so Mercie's adventures eventually caused a series of unusual events to unfold. One of those days, when she was tired, shrunken, and as desperate as ever, and still preoccupied with strange thoughts, something very special happened to her...