Garland can't possibly block all of it. It's clear he's hurting, and yet he seems unperturbed by the fact that he's being torn to shreds, retaliating with a [Wave] of energy that scythes across the deck and into Frisk. "You are a child that knows nothing about him."

He waves a hand, conjuring wisps of thought, scenes from Terra, from Gaia. Kuja snarling, standing over the corpse of a beatiful, familiar, and dead dragon, kicking her in an attempt to rouse her. Kuja, stepping over the charred corpse of a Burmecian, an army of black mages marching around him. Kuja, rising into the skies over Terra and unleashing Ultima, burning everything. A familiar voice, caught in a choked laugh that turns so quickly to sobs, and then to silence.
"I won't let it happen.
I won't... I won't let this world exist without me!"

"The mere notion that he was mortal sent your 'friend' flying into a tantrum that ended one world and nearly ended all. You aren't even aware of the depths of atrocity he's committed." Another spell cast, and one of the Frisks finds themself frozen, [Stop]ped in time. "Whether I find it disgusting or not is irrelevant. He is a mistake, one I failed to correct. You know what threat is posed by the forces arrayed against Vaikuntha. Will you make them pay the price for your defense of a broken doll guilty of genocide?"