Do you fear me?

[Leanne]

Feast upon the shine of my blade!
For I see the fear upon your lonesome eyes. -- lonesome eyes? Surely they've got one another to keep them company? Seriously, how do you see fear "upon" any kind of eye?
Besieged and imprisoned by the weakness you hide. -- fear is imprisoned by weakness? Wouldn't that make fear weaker than weakness?
But I shall not be fooled! -- fooled by what? The weakness that you can't see because it's hidden, or the fear you can't see behind the hidden weakness that's holding it prisoner?
I laugh at you, instead. -- probably a good choice. I'd be laughing at this point as well
Therefore, you're a critter. -- so you're sneaking up on a weak (but hiding it), scared (but hiding it even deeper) raccoon or something?
A weak, plain, critter. -- no, not a raccoon, something with only one colour. Maybe a rather dull possum.
So you shall die this very second; -- it's taking you more than a second to complete the threat -- poor thing's died of boredom or fear or weakness by now
For my eyes can bare no more. -- bare no more? Were you holding open your eyelids with something? No wonder you can't manage it any longer, that must have been quite painful.
Hideous as you may be, -- ugly, dull, weak, scared, but quite good at hiding critter
Thee, will die bold. -- misuse of "thee" -- if you must use an archaism (and presumably you must), then this should be "thou". I'll bet the critter is happy that its death will be bold, after all that weak hiding it's been doing