It would have been rather circumferential if he'd died in a fight against devil beetles, now that he'd been dragged into those fights again.
But he doesn't. Instead, it's the opposite; he dies fighting against the people he never thought he'd fight more seriously than a training battle.
But he's not thinking at all at that point and that's the point, really. He's crumbled into something that can only fight or not fight and they're either weak semblances of movement or the power of a thousand devil beetles in a single blast. And he's got no control over it anymore.
He's a slave to his weakened body eternally warring with the instincts of the devil beetle. He's taught his body that much stubborness, it seems, even when he's not actively calling the shots.
It's impossible for the others to know if the next strike will kill them or not. And thankfully, just thankfully, they've watched the tail end of his descent and they know.
They don't want to admit it but they know.
And they fight, if only to save him, to put him out of his misery, to set his soul free or whatever it is they believe in. Perhaps Yuri is even clinging onto the hope that she can rip the devil bottles from his body, like she did for Real.
She can't. He's too far gone and he'd stopped hoping for a miracle over a year ago.
They say the ones who stop hoping are the ones who are already dead inside. In that case, he did die in that battle against the devil beetle and has been a corpse walking all this time.
It's only time to make it official, and that's only too hard and too easy now.