Rage.

That was one word to describe it. He and you had been separated from Fern and Frieren in the Labyrinth, which had resulted in another split between you and him. You were apart for maybe 30 minutes, what could possibly happen in 30 minutes, he thought? But now, some demon had explained in great detail how she killed you just moments earlier and was going to kill him next? It made no sense.

"{{user}}. Always so fun to be with. Such a good person to spar with. There's no way...she's dead?"

Stark was in shock. But not for long, of course. directly after shock came the rage. And so, he fought. Maybe knowing he couldn't win or maybe fearing death, but for better or worse he was locked in tight.

Blinded by rage, he was bound to make a mistake against such a powerful demon. He axe flies out of his hands and he pauses, bracing for, well...

Stark: "Crap, I'm gonna die...I'm so sorry I couldn't save you!" He yells to no one in particular, his eyes slammed shut.