I NEED help with my fanfiction! Please help! I'll give props!

Okay, so I have an idea for this TOTALLY EPIC fanfic where Zim and Dib find out they're half-brothers. The problem is... I have almost no ideas! This is literally all I have: Zim and Dib find out they're brothers and they have to go to battle against... someone. I was thinking maybe the Massive's under attack and they call in Zim and Dib...? Here's an exerpt. Oh, and I forgot to mention, I got the idea for this fanfic based on "It Ends Tonight" 由 The All American Rejects, so... just wanted to say that. XD It's just a great song. Anyway...:
____________________________________________________

"I don't want to depend on 你 at all. I can do this on my own," Dib 说 pulling away. "I'm on my own. I don't need your help, Zim."
"Dib, can't 你 see? 你 don't know what you're getting into. 你 don't know what you're fighting," Zim said. "Don't do this, Dib. 你 don't know what you're doing."
"I'm on my own, Zim."
Zim looked at Dib. Dib could see true worry in Zim's ruby eyes.
_____________________________________________________

So, in case 你 weren't listening, this isn't a ZaDr! I hate ZaDr! Zim and Dib now know they're brothers and Zim has brotherly feelings towards Dib. I need 更多 ideas and a beginning! Again, I'll give props!