A friendship that blossoms out of adversity in their struggle against the Abyssal Fleet.
The truest of friendships come from adversity and overcoming it, both external and internally.
Despite their differences, and maybe in a way because of them, they are able to fight side by side to defend their lands. True international cooperation.
Or someone go their and give their handshake a strength test. As I like to imagine, millitary style hand shaking between opponents always involves cracking sound from joints, tense muscle and bruise hands.