The battle between the goodguys and their white Kampfer enemies, which you see the setup for at the end of the last Kampfer OVA, has begun... and they're trying to get the MC over to their side too. And they've upped the stakes by saying that if the MC decides to stay a girl and chooses them then his friends (the other blue/red Kampfers) will die, but if he chooses to stay a boy and his current friends then the white ones will die... and dead Kampfers apparently become forgotten or something, so people who aren't Kampfers probably won't even remember who they were. That seems to be the case, anyway, if the people are telling the truth; I'm not 100% certain on it, but probably. Of course I'm sure none of the goodguys will die, and they might find a way to avoid killing their enemies too who knows, so I'm not expecting such depressing things to actually happen. Still though, even just at the level it's at now it's more serious than the anime. I like the anime's tone myself, though... nothing wrong with a happier version of the story!
But even in the manga I'm not expecting grimdark, certainly, but the setup is one where they could go that direction if the writers want to. I don't know how the novels go... hopefully they get out of this war somehow without having to kill the white Kampfers. The MC and Akane are certainly around to the end, and President I'm pretty sure, but I don't know about anyone else, or how the story does apart from that Akane apparently does win (main girl wins, how shocking).