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" bởi The All American Rejects, so... just wanted to say that. XD It's just a great song. Anyway...:
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"I don't want to depend on bạn at all. I can do this on my own," Dib đã đưa ý kiến pulling away. "I'm on my own. I don't need your help, Zim."
"Dib, can't bạn see? bạn don't know what you're getting into. bạn don't know what you're fighting," Zim said. "Don't do this, Dib. bạn 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.
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So, in case bạn 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 thêm ideas and a beginning! Again, I'll give props!