When they arrived, they saw Sebastian already there killing demons left and right. There had to be at least several already dead before Cassian shot one that was going about to claw Sebastian when he couldn't see it. Sebastian turned around to face them while still trying to face the demonic horde. "I can deal with these bastards myself. Head back to the Union, and you can go back to... do whatever you usually do."
It wasn't even a second later before Cassian yelled back at him about what he was doing, risking a possible rift to occur, not even bothering to teleport them to somewhere more secure. But Sebastian didn't seem too worried about it. "Sounds like a party." He joked before using a knife to stab a smaller demon in the chest before ripping the knife out.
"Do you not even care!? I would've thought people there would actually care more about the people and the risks of this!" Cassian shouts, which got another cocky reply from Sebastian, "If a rift appears, then that's just nature calling for me to get back down there." The demonian chuckles at his own joke before killing another demon, thinking it was the last one. He hears the sound of something approaching him, so he turns around, ready to dodge the actual final demon's attack. Only to receive a swift left punch from Cassian.
Sebastian was able to react just as quickly when he also gave Cassian a knee straight in the gut. Cassian takes a couple steps back while Sebastian shakes his head with the two looking at the other. For Cassian, he was looking at Sebastian with annoyance, rage, just about any average feeling anyone would get from someone not taking what could happen seriously, especially in this situation.
Meanwhile, Sebastian looked down at Cassian with a smug look. His face was filled with glee, actually seemingly ready to have some fun with this. "So it's really a party now, eh?" He continues to joke, which garnered an irritated response from Cassian. "If I gotta kill you to stop you from being this stupid, I will." The threat didn't seem to get to Sebastian that much as he readied his knife in his hand.
"Really? You want to try that? I'm pretty sure we've already gotten an idea on who'd win between us. Now, if you really want to, I'm sure I could kill a few doing this." The situation was escalating, and none of the other three knew really what to do. But Cassian told them to not do anything, let him deal with the bastard. Meanwhile, Sebastian joked for them to contact Gris, or the Union, he didn't care which one. But to still remove whatever corpses they could.
He even decided to tell them that if they don't want to do anything, just enjoy the show that they're about to make. "Alright, blondie, let's have some fun with this. And no guns to make things a bit more interesting." Cassian actually agreed with that idea for one reason or another before he grabbed his own blade to stab Sebastian, only to fail at doing so when the latter was able to use his knife to block the attack. Sebastian was able to easily overpower Cassian before pushing him away.
"It's no wonder you decided to go out on your own, I don't think anyone would appreciate the deadweight they'd have to be carrying around," Sebastian taunts once more, enjoying his own bit of banter, and he actually smirks at how Cassian responded to him. "And I don't blame your brother for leaving you. It's almost like you take it as an achievement when you mention his problems. I wouldn't be at all shocked if you were the reason for it all."
As the two continued their duel, the three were still getting rid of the corpses, but knowing what to do about them. Inevitably, they decided to call for Gris' help since she could easily be a neutral party. "Aww, I'd love to help with their little scruffle! But I'm here winning in cards against some others. Even beating Garrett! Ye all remember him, yeah?" Her joking tone made Sebastian's own attitude look like nothing.
Though, Gris did say that she was going to send someone else before she stopped responding to them. Meanwhile, Cassian finds himself on the ground, looking up at Sebastian, who taunts him. "You couldn't have even lasted that long? No wonder you're single." "And you can't keep your mouth shut. No wonder you're single."
The exchange actually got Sebastian to chuckle, but he'd find himself frowning soon enough when he'd see Cassian pull out a grenade and throw it above both of them. While the actual blast didn't do too much to either party, it still pushed them back away from the other. Sebastian shook his head before he saw another item thrown. He thought it was another grenade, but it was a smoke bomb.
Despite the smoke surrounding him, he looked all around, trying to be ready for whatever would come. Yet that wasn't enough for him to evade the tip of Cassian's sword slicing over his left eye. He backed away in pain as he covered his eye, feeling the blood drip down. He had no idea what to do. Only made worse when Cassian walked out of the smoke cloud. Sebastian's breathing got more rigid, but he still decided to laugh at the situation. "Must be your lucky day."
Cassian was in actual shock at how Sebastian decided to continue fighting him despite the fact that he was pretty sure he lost his depth perception, and Cassian was actually right in his assumption. Even though Sebastian thought he was right there, Cassian was actually a bit off from where he was. But Sebastian was still close enough that Cassian had to dodge each of the attacks that were thrown at him.
Cassian still had some offensive showing, but he wasn't sure what to expect. Especially when Sebastian was able to not only parry one of his attempts at a slash, but being able to parry it while punching him clean in the jaw. The two would still continue their fight with them both getting cuts on their bodies, but Sebastian was the one more on the defensive of the two. And it stayed that way with them both going around the abandoned building's interior in their fight, all until they felt the ground around them begin to shake.