Try settling things peacefully.

Kazuma then noticed that the townspeople were giving Megumin the stink eye as they slowly realized that she would have to be the culprit. She looked around as if to find another potential patsy, but lowered her head in defeat as she failed to find anyone. She then stepped forward, and was about to speak up, before Kazuma put a hand on her shoulder.

"Don't say anything stupid, let's try convincing him to leave us be, whatever he demands within reason, we oblige, got it?" Kazuma asked. Megumin hesitated, before nodding. Then, remembering Aqua's hatred for the undead, and that she might screw this up, turned to Darkness. "Go make sure Aqua doesn't provoke him further, would you?"

"Got it!" Darkness said, quickly going into the crowd, and looking for the goddess.

"Well!? Is no one to confess!?" the Dullahan demanded, before Kazuma and Megumin stepped out of the crowd.

"Apologies, it was us... Or rather, her," Kazuma said, pointing to Megumin. "I was just carrying her back to town after blowing off some steam."

"Yes, I am the explosion mage Megumin," Megumin replied, trying to sound calm. "I'm the one who has been trying to blow up your castle."

"Oho, one of those Crimson Magic Clan people with their weird names," the Dullahan remarked, making Megumin sputter about how he insulted her name. "Tell me! Why do you torment me so?"

"I swear, it's not intentional!" Kazuma quickly spoke before Megumin could say anything stupid. "We had no idea the castle was occupied, and she's... Well, she's an explosion nut, and since we don't have any quests to do at the moment, she was just casting the spell for the hell of it at what we thought was an abandoned castle! If we knew someone was in there, let alone someone as powerful as you," he added, trying just a bit of flattery, "Then we would have found another place to do so. We still could, if that helps!"

"Humph. You are in luck. I had only come to warn you against continuing your foolish attacks," the Dullahan replied. "I have taken up residence in that castle temporarily as part of an investigation. So long as none of you interfere, I will leave you be. But so help me, if I hear one more explosion!"

"You won't, I swear!" Kazuma said hastily. The Dullahan got back on his horse, and left, muttering about fools and interrupted naps. Kazuma sighed in relief. That had gone much better than he had expected.

"Now we have to find somewhere else to blow something up... And I was so close to doing damage to the castle, I just know it!" Megumin pouted.

"Shut it. We're lucky he was so willing to let it slide," Kazuma chided her. They then went to find Darkness, who, sure enough, was restraining Aqua with a hand over the furiously struggling goddess's mouth. "The Dullahan is gone now Darkness, you can let the idiot go," Kazuma said.

"Idiot!? You should talk, why the hell did you let that Dullahan go!?" Aqua ranted the moment Darkness released her.

"...let him go? If anything, he let US go," Kazuma deadpanned.

"I could have taken him! Then we could go back to doing some normal quests!" Aqua asserted. "You know how effective my Turn Undead spell is against such foes! It would have worked on that lich if you didn't interrupt it!"

"Yeah, thing is, the lich wasn't fighting back," Kazuma pointed out. "And I easily disrupted you with a smack upside the head. Do you really think you could have destroyed that guy before he had the chance to eviscerate you?" Aqua paled as she realized exactly what Kazuma was saying. "That's what I thought," he said.