I'll keep it short 
1) Im is the devil or he has the zoan of the devil, and the devil is the personification of pure evil
2) The only people who can face evil are those with a strong spirit or will, which helps them fight against it
3) In one piece, the personification of the human's will/spirit is... the haki!
4) One day joyboy (or someone else maybe?), discovered that and he tried to use the human's spirit/will in a fight. Then, he called that thing... "haki"!
But only the strongest will/spirit among the strongest spirits/wills can face the the devil's power, so we can suppose that only the strongest form of haki is the real key to fight the devil and defeat him!
Joyboy was so strong and so skilled at it that he learned to imbue it into weapons, allowing others to fight the devil as well! Even if they can't use that haki!
I know what you're asking yourselves: kaido and big bom are controlled by their evil, they are evil characters after all... so can they face evil? Can an evil "king" among humans, fight the evil?
6) In addition to all this, we can also say that only the one who is truly free can be saved from the influence of evil and truly fight it
More u are free, more your spirit/haki is strong!
And who is the freest man? The man who wants to conquer nothing!
And who is the freest human being in history? Who wants to free the world? Nika! That's why im fears him so much. He is the only one who can truly defeat him! He has the strongest haki in history, because he is the freest human being!
Humans can try to fight evil with the help of a few strong humans, but only him can defeat the source of evil... the devil himself!
The fruit of nika was born because people dreamed of being free from the concept of evil (evil kings, evil parents, evil friends ecc ecc) and living their lives as free people!
What im feared the most is the human's desire for freedom!
Thx
1) Im is the devil or he has the zoan of the devil, and the devil is the personification of pure evil
2) The only people who can face evil are those with a strong spirit or will, which helps them fight against it
3) In one piece, the personification of the human's will/spirit is... the haki!
4) One day joyboy (or someone else maybe?), discovered that and he tried to use the human's spirit/will in a fight. Then, he called that thing... "haki"!
But only the strongest will/spirit among the strongest spirits/wills can face the the devil's power, so we can suppose that only the strongest form of haki is the real key to fight the devil and defeat him!
Joyboy was so strong and so skilled at it that he learned to imbue it into weapons, allowing others to fight the devil as well! Even if they can't use that haki!
I know what you're asking yourselves: kaido and big bom are controlled by their evil, they are evil characters after all... so can they face evil? Can an evil "king" among humans, fight the evil?
6) In addition to all this, we can also say that only the one who is truly free can be saved from the influence of evil and truly fight it
More u are free, more your spirit/haki is strong!
And who is the freest man? The man who wants to conquer nothing!
And who is the freest human being in history? Who wants to free the world? Nika! That's why im fears him so much. He is the only one who can truly defeat him! He has the strongest haki in history, because he is the freest human being!
Humans can try to fight evil with the help of a few strong humans, but only him can defeat the source of evil... the devil himself!
The fruit of nika was born because people dreamed of being free from the concept of evil (evil kings, evil parents, evil friends ecc ecc) and living their lives as free people!
What im feared the most is the human's desire for freedom!
Thx