First, as a fantasy anime/VN fan, one thing you'll inevitably run into are these two words... 'yuusha' (勇者) and 'eiyuu' (英雄). The problem with these two words is that they inevitably end up translated as the same thing... 'hero'. However, the nuance of each word is dramatically different, at least for those of us who actually care about nuance.
Now, 'yuusha' is a word you hear mostly in certain types of fantasy VN or anime... these include 'sent to another world' and 'classic swords and sorcery fantasy', but can include things similar to Power Rangers and games like Venus Blood. The usage of yuusha generally refers to a 'chosen' individual who is stuck with the duty/obligation to confront a force that is beyond the capacity of normal people. Demon Lords, kaijin, insane gods... you name it, it probably has a swirly target sign that only a yuusha-type hero can see on it. There are 'evil' yuusha (mostly in dark VNs), but for the most part, they are pictured as being on the side of 'good' pictured as a near-absolute concept.
'Eiyuu' is a bit different. The concept of 'yuusha' can't really be applied to a real person, because the real world is almost never unambiguous enough to allow for the term to be usable, but the concept of an 'eiyuu' can be applied to real people. War heroes, great military leaders, rulers that lead their people to victory against an impossible foe, men who turn the tide of a war, etc. fall under this term's aegis. As an example, Valzeride from Silverio Vendetta falls under the aegis of this word, as does the insane loli in Youjo Senki. It is much easier for an eiyuu to be evil, because all an eiyuu needs to be is glorious to a group of people. They don't need to be moral or upright... or even seem so.
Really, this is just a commentary on how confusing Japanese words that translate the same can be... and it might give you all a hint as to why some of us say that 'Japanese translation is an oxymoron.'