Okay, ignore everything in the manga/series that has anything to do with how Kenshin came by his reverse-blade sword. In this little ficlet, it didn't happen. Keep that in mind, and hopefully things make a little more sense. I see this little story as kind of a mix between The Velveteen Rabbit and Pinocchio, only with swords.
Sword
It had been forged lovingly by a talented craftsman years before he ever picked it up. At the beginning, despite its maker's skill, it cursed the hand that had shaped its dull edge, before it knew its destiny in the hands of a red-haired swordsman.
The blade had known love at the end of its maker's precise craft, having been elegantly designed and remarked upon as a beautiful rarity by the maker himself. And then, things had changed. Having declared the blade finished, the maker turned to other works, setting the blade aside in favor of new lumps of metal waiting to be transformed by the maker's touch.
After its creation, the blade lay cradled on a stand, watching jealously as other blades – sharp along the outside edge – were forged in the same fires of its own creation, and then sold off to new masters and new destinies almost before they had cooled.
The few blades their maker had not immediately sold sat near it, leaning in corners or across the maker's workbench and insulting the backwards blade, as they began to call it. As one after another perfectly sharp blade disappeared from their displays, the backwards blade fell more and more into a state of despair. The other swords had labeled it as dull and imperfect – not even worthy to be labeled a sword. No master would want it, and the blade would stay on the maker's shelf long after its siblings had led long lives serving the masters who were so eager for their sharp elegance.
The blade's outsider status caused it to lie unused and unwanted for a long time, gathering dust and the ridicule of those who viewed its body. Such disinterest showed it by potential masters caused the blade much bitterness until it came to regret its uniqueness and fell into a deep sleep, cursing its fate to always be different. Years passed, and then something happened.
It awoke with a start, disoriented as its body was pulled out of the darkness of its plain sheath and sent waving about in the air in a practice kata. Sunlight touched its edge, causing the backwards blade to sparkle with a beauty it had rejected in itself.
After bracing itself against the harsh words that were sure to come of its uniqueness, the heart of the blade skipped as it realized that this one buyer was different. It had not been belittled as backwards yet, and the man holding its slender body seemed to smile, as its maker had upon first meeting. Its edge rose, guided by his hand, and it rejoiced upon first view of the one. It yearned for this man as its new master, but it struggled to suppress the hope that rose as the man frowned when a price was named. He sighed, and hefted a small coin purse in one hand.
Sure that it would be retired to the back of the shop, the blade was surprised to feel the man's hand clench tightly around its hilt. This hand was strong and sure, and the blade sang in delight as it once again found itself soaring around the yard, expertly guided as it wove through the air in a slow, careful dance until it slowed, body raised until the backwards blade lay level in the man's hands. It would have cringed if it could as the man's eyes took in its flat edge and simple hilt.
"I will have no other. This sword is perfect." The man said, and nodded once at the blade before sliding it back into the darkness of its sheath. If it could have, the blade would have smiled to itself, as the bitter memory of every rejection faded in the presence of this man – the master who had deemed it perfect.
