Frisk's expression is frozen for a moment as their character processes that information slowly, looking it over, turning it up and down to find any reason for Cassius to be lying. A look of dawning horror twists their face, and they clap a hand over their mouth, trembling slightly. Maybe a bit overwrought? Well, their brother had just died, so it was probably a good idea to roll with the melodrama.

"I... I see. At least he didn't die on the b-battlefield." Frisk gulps, trying and failing to maintain their composure. "That's... He..." Unfortunately, Frisk isn't a skilled enough actor to cry on command, but they can make a convincing enough pantomime of it. "That's not--"

They break character for just a moment. "Here's where I'd lunge forward to hug Marcus and seek comfort from him, but that would be a bit awkward right now since we're seated across from each other so just... assume I'm doing that. I'm also assuming that Minfilia's just around my age, maybe a bit older, so that's influencing characterization. Kids don't deal with loss well."

Putting their game face back on, Frisk resumes their gross "sobbing." "That's not fair! It's... it's not... He'd won and he's a hero and he deserved to come back home and he died because of a stupid boat and it's not fair!" they wail.