I am working on the information for a fantasy novel I wish to begin soon, and I'm struggling with one part of my plot... The plot is... This story is about a forbidden love interest between a human and a vampire. The story begins inside a castle of vampires - in a training arena. The female vampire - who is a highly trained and dangerous assassin - is to be paired with a human sent to be trained into warrior. The question is, how can an assassin train a soon to be warrior, especially human? The "bolded" section is my concern... is it possible for a female vampire assassin to train a male human into becoming a warrior?
Possible? I'd say in a fantasy novel pretty much everything is possible... the only limits are those set up by your own imagination.
Vampires in most stories can live forever baring sunlight and stakes to the heart. A vampire that has lived many more years than a human can live and has lived much of that life as an assassin probably has a lot to teach a warrior in training about combat.
Think about the vampires life before she became an assassin. Was she a soldier, or other warrior type? Also, I expect an assassin would be trained in all kinds of close combat, in the event they had to resort to brute measures to escape or accomplish an assassination when the subtle approach didn't work. Makes sense that she would have a lot to teach.
Why would it NOT be possible for a female vampire to train a male human? What would prevent that from happening in your story? If your answer is "Nothing, I guess," then go ahead and let it happen.
Is it possible? No. There is no such thing as a vampire. What you really mean is, Can I sell the idea to the reader? That all depends on how convincingly you write it.
I'd say it makes sense for an assassin to train a warrior, although warriors are used for different purposes usually. It depends on the setting, in a modern day setting it would make perfect sense for an assassin to train a warrior, they'd know how to avoid being spotted, how to wield a weapon, etc. In a medieval setting it would make less sense, assassins tend to be trained in more short range or stealthy weapons, whereas warriors are typically trained in power over finesse.
Fantasy doesn't have to obey ANY rules. You make your own. The characters never lived, nothing of such has ever happened, the world doesn't exist. You are free to lay down anything you want. If that assassin wants to train a frog to become a master chef I say there is nothing stopping her from doing so. The same goes for your question.
Just because she is doing the training doesn't mean that she wants to do it.... I like your idea and think it makes sense. A vampire would make an excellent trainer for a warrior for sooo many reasons including; Patience, they live for ages so time is a different experience for them compared to a human Vampire abilites (whatever they may be), push the human to be more than they thought possible Assassin skills, added ability to do what needs to be done, without emotion etc may be the very reason the vamp is able to work with humans I guess it would be a really intense training.... Do all the warriors survive? If you can come up with enough answers to the question 'why?' you'll have no problem. You world is only limited to the walls you build around it Good luck with it!
Give the vampire a unique personality. And the woman. It has good idea potential. Just execute it well with your imagination.