Kang Oh wanted them to defeat the boss monster, even though the Empire Guild was watching and that they'd specifically warned them not to. 

"I'm not doing it. Definitely not!" Sephiro replied. 

'The Empire Guild's one of the 5 great guilds and they're known to return the favor twofold. Why would I do something as stupid as going against them!?'

"Hear me out first. I have a terrific plan."

"I told you, I'm not doing it," Sephiro said firmly.

"I'll reduce the number of times you have to help me by one."

Kang Oh laid the bait.

"I'm still not doing it!"

But he didn't bite.

"I'm not doing this for myself. This is all for Eder's benefit," Kang Oh said. 

"You're lying!" Sephiro and Eder simultaneously yelled.

This was Kang Oh they were talking about; they couldn't fathom him doing something for someone else's benefit. It was definitely a lie. 

"Kainshell's boss monster, Clovis, drops the Hellfire Mace, which is the best weapon that Eder can use at this point in time."

He was being completely honest. 

Not only was the Hellfire Mace an 'undead only' weapon, but it was also the most powerful...