A troll perhaps?

"Wait... To keep things fair... Trade blades with Kazuma," Aqua cut in.

"What? I thought you said Ounce was useless to me," Kazuma blinked.

"It's called Gram!" Kyouya snapped. "...and why Aqua-sama?"

"You can still use it as a regular sword, and it won't exactly break," Aqua told Kazuma. "Plus, if the idea is really for you to walk in Kazuma's shoes for a bit... It should only make sense that you don't get your original cheat item for the duration..."

"...I suppose you're right," Kyouya agreed after some consideration, and handed Gram over. "So long as I'm assured that I'll get it back."

"I'll bring it back," Kazuma grunted. "I'll even tell you where we're going when we pick a quest, so you can always find it again if we end up failing."

"This troll one looks doable," Cremea noted. "They're big and stupid enough that Kazuma's tactics should run circles around it."

"Kill the troll roaming around the wilds? Yes, definitely doable!" Fio agreed.

"I suppose that's settled then," Kazuma nodded, buckling Gram to his belt as they got going, leaving Kyouya to pick up a quest with Kazuma's original party members.

"...that was a mean prank you pulled on Kyouya," Fio remarked at Kazuma once they were out of earshot.

"And that's HER saying that!" Cremea snorted.

"Hey, I take no pleasure in it," Kazuma bullshitted. "He just needs a hard lesson or he'll never leave me alone..."

"...then wipe that sadistic grin off of your face!" Fio giggled.