Kamui never meant to love Fuuma. Or rather, Fuuma was all he meant to love: his childhood friend, his staunch protector.
Not this travesty, this "Dark Kamui," so much crueler and harder than Fuuma could ever hope to be.
Kamui never meant to love Fuuma's darker soul, but that didn't stop it from happening.
Fuuma never cared about destroying humanity. All he ever needed was Kamui's attention, and he got it any way possible.
Courtship is so much easier when you're a sociopath. You simply let it be known you're interested, and then kill anyone who gets in your way.
Fuuma never expected to gain Kamui's love, but why argue with what works?
It was Kamui who came to Fuuma, the first time, ostensibly to challenge him, but it quickly became something significantly less violent, though no less heated.
Kamui didn't go home that night.
Kamui didn't go home for a week.
Sorata blamed Fuuma, tried to attack Fuuma, and was shocked when Kamui came to fight instead. Shocked more to learn that the old Stargazer was not always right, and his life would be given for (to) Kamui.
Sorata lost.
The Seals weren't ever sure what happened.
The Seals died mostly painless deaths.
Only Subaru survived, but then, Subaru has never cared about the fate of humanity, and as long as Seishirou's around, Subaru will continue to not notice the world.
The Angels didn't really care. Yuzuriha's death broke Kusanagi, but the rest of them had broken long ago. The Angels sat back and watched.
Kamui never meant to love Fuuma, but nothing will stop him now. Fuuma never expected to gain Kamui, but he's not about to let go.
In another lifetime, a twisted hate might have saved humanity.
Here and now, a twisted love will destroy it.