I feel like I could win
In a fight against a hundred men
Winning such a fight would be an obvious symptom of invincibility, therefore the feeling of being able to is a symptom of feeling invincible.
You just imagine
What I would do to them
Many who feel invincible share their feelings with others, imagining what they would do if a fight were to ever break out.
Call it a guardian angel if you like
Call it plot armor if you don't
Perhaps the speaker has already been in a few fights and won, doing nothing to improve their cockiness. The speaker doesn't care what whoever they're talking to chalks it up to, whether it be guardian angels or plot armor (something that characters who are important to the plot of a story seem to be wearing, making them impervious to any real harm). I personally believe in guardian angels (I don't act recklessly, one should always take care of oneself).
You may back down from a fight
But you know that I won't
Perhaps a friend or relation of the speaker is now trying to dissuade them from getting into any more fights, but the speaker refuses to listen, of course, feeling invincible.
I will never die
Never dying would be a telltale sign of being the main character.
'Cause I'm the main character
The reason behind all of the odd lines of the chorus being true would, of course, be main-character-hood.
I can do it if I try
Being able to accomplish anything with nothing but "really trying" is also a telltale sign of being the main character.
'Cause I'm the main character
The universe is mine
The universe has great things in store for the main character, often in the form of "destiny" or something like that. In some cases, the universe seems to simply belong to whoever the protagonist is.
'Cause I'm the main character
And they'll never know why
The people around the protagonist, or the "side-characters", realistically will have no idea why the main character is always faring so well.
'Cause I'm the main character
We both know I'm dead inside
So I look death in the eyes
The main characters of some very violent stories should realistically be dead inside at least to a degree, thus enabling them to stare death in the eyes, unfazed. Violent thoughts of fights breaking out will also desensitize the speaker.
Somewhere, a part of me understands
That I'm not what I think I am
Perhaps the speaker has a nagging feeling in the back of their head. "You're not really invincible," it says, and it's right.
Call it a guardian angel if you will
Call it plot armor if you won't
When I go in for the kill
I'll do what you don't
The speaker's friend, being (to the speaker) a side character or deuteragonist, but in reality just less dead inside, won't go in for the kill the way that the speaker thinks that they can.
I will never die
'Cause I'm the main character
I can do it if I try
'Cause I'm the main character
The universe is mine
'Cause I'm the main character
And they'll never know why
'Cause I'm the main character
I'm the last man standing
I'm on top of the earth
The smoke fills my nose
Was it really worth it?
The fire burns my eyes
I behold my beautiful prize
The world cut in two, no, it was three
And it's all because of you, no, it was me
The bridge cuts do an even darker reality where the protagonist, instead of perhaps being a hero, simply wants to be the strongest or the best at something, sometimes burning down whole worlds to get there.
I will never die
'Cause I'm the main character
I can do it if I try
'Cause I'm the main character
The universe is mine
'Cause I'm the main character
And they'll never know why
I will never die
'Cause I'm the main character
I can do it if I try
'Cause I'm the main character
The universe is mine
'Cause I'm the main character
And they'll never know why