Hmm...You wanna story?
This shows some promise. If anything, it's got a spot in the portal for sure, but it needs prudent sequels.
You wanted My idea? Here's one:
"Luigi joined up with Sonic a while back without Mario ever knowing of it and is actually a spy for an intelligence group. Since he caught up with Mario and Sonic, he had no choice but to shoot his own brother. Failure to do so would show that he'd become a traitor in favor of Mario...
The reason Luigi sided with Sonic is another story, however, Mario makes an attempt at forcing his brother Luigi to tell him what's really going on. As Sonic (The real Sonic) sees these events unfold, he Calls out Mario and thus begina an epic battle... Luigi promptly leaves the scene and views the battle on a monitor from an enclosed secret area, planning to use a secret he has planned out since the beginning... ..."