Heroic's just another way of saying BRASS SECTION
It seems from the last comment that you're supposed to make this for someone's flash?
I have 2 suggestions for making this more heroic without much reworking
(1) it needs to build faster, because VGM doesn't get the luxury of long build-ups. I'd suggest a quick transition at the 0:10 mark.
(2) After the transition, you should go for brass section backing. The timbre of Brass instruments is just pure win, and it'll detract from that despair-ish feeling.
If all else fails, you might just have to change your chord progression. It sounds like you're basically staying in harmonic minors all the way through, and if you transition to a major or a melodic minor you might change that. But I know you don't want to go back and re-write, so maybe just try the brass?
Hope it turns out well!