Well I guess I need to share with y'all the most recent events of my Weds night campaign, where it looks like Sumiko's days of descending into evil might now be over.
On our quest to find allies to help us prevent the appearance of the demon god in two years (game time), we went to a city that ended up being populated by lots of good orc monks + angels. They also had their own planar gate (to their dimension of heaven) there. We were trying to gain their help and maybe an army.
Our group had a mix of alignments -- a few good, a neutral or two, and then two evils. One was Sumiko, who spiraled into it but projected as "pragmatic". The other was Tristan, the strix, who had been converted to Chaotic Evil when compulsed to release the demon lord of magic.
We left Tristan in the brig as usual (because he's evil and can turn people against us by association) when we went to talk to the angels and ask for help. They were kind of stand-offish and skeptical, and Sumiko found them condescending and had trouble keeping her beak shut.
After ten days of us improving the ship, hanging out, buying supplies, they came to our airship and demanded that everyone come off and give an account of who they were. So the group basically complied, but this made Sumiko bristle. (She has had bad experiences with angels. The last angel, in the soul gem she found, was difficult to deal with; and when she finally let him out, he was arrogant and insufferable.)
Last, we marched out Tristan, who they immediately demanded destroy his holy symbol and that he be taken into their custody. The elf negotiating with them from our group said, "uh, no, he's in our custody," and the angel in charge there sic'ced the 20 monks surrounding our group on the elf and Tristan. They were grappled effectively and the rest of us were threatened within that closing circle. Tristan was struggling (although not succeeding in casting anything or getting out, it was all pretty inept), so the angel cast Holy Smite on the group, which hurt Sumiko and some of the others who had not done anything wrong. (Police brutality!) Sumiko used her psionic wall-walking power to run up the side of the airship to the top deck, to get away; a ninja tried to hit her with a throwing star and missed.
Down below, the angel was still smiting things and then walked up and hit Tristan over the head with the pommel of her sword. (Note that no one else was fighting, but even the elf spokesperson was being treated roughly -- they were going to drag he and the strix off to the tribunal, to be tried and punished.) Meanwhile, now Tristan was uttering about how his god was really going to give it to them.
Furious at her friends being treated so unfairly, and being outraged by the angel's arrogance -- the arrogance of all angels -- Sumiko (unobserved atop the ship) grabbed the big soulstone out of her bag, the one she had never dared use before, the one that terrified her. The creature inside, the balor demon (essentially a balrog), spoke to her, and she was so angry that she channeled its power while letting the balor decide how that power would be made manifest. She was used to struggling for control with the angel, but that is because the angel and she were at cross-purposes; here, the balor was all too happy to comply. She rolled a 39 on UMD, and the balor's power poured forth from the stone.
The angels and monks did not know what hit them. The balor uttered a horrific Blasphemy, some of the party took damage (the good members) but fortunately made their saves; yet many of the monks and even the angel failed theirs. Dead, blown away, turned to ash, whatever. Sludge. Even any who made their saves were paralyzed for minutes. It was the most horrific display of power -- the instant death even of powerful divine creatures -- that anyone had witnessed. It was a total WTF just happened moment, as no one down there even knew it was coming.
Every survivor freaked out and scattered. The party threw anyone still paralyzed back on the ship. Some thought Tristan had done it (and he was still lying on the port below). The ones that suspected sumiko found her curled up in a ball in the corner of the deck, shaking. When they threatened her, Carnage (her gnome thrall) stepped into defend his mistress... and it was quickly clear to them that she was in no shape to do anything like that ever again. The decision was made to cast off. The balor stone was tossed on the deck below (let the angel leaders decide what to do with it) with Tristan, kind of pinning the crime on him, and the party sailed off to get as far out of Dodge as possible.