I think it's obvious why Phobos and Deimos accompany Ares to battle. Those who fight in battle instill fear and terror on others, but they feel those same emotions too.
Now of course, these two are born out of love, Aphrodite. Love for your people, who you might lose, by your death or theirs. Love for what you're fighting for, whatever that may be. Love for yourself, the most dangerous thing you can lose when you're blinded by emotion. And even love for your opponents, because maybe you truly don't want to hurt them.
Love makes you afraid for what you might lose in life, a constant battle with your surroundings and yourself.
Almost nothing is more terrifying than love. What if you lose everyone? What if you don't lose your people, but your love itself? What if you never get to have it? Or even scarier, what if you do?
The constant battle of living and the inevitable need for love we have is the most terrifying thing in the world. But is that not what we are?
Of course Aphrodite and Ares had Phobos and Deimos. It's nature.












