There are side missions to every one of the gunslingers.

 

Vash or any other name you call him.Destroy Knives.

 

Brendon/Gun grave:Destroy Gangs boss.

 

Spike/bebop gang:collect bounty.

 

Gene Starwind:protect malfina and the ship.

 

Zero: Protect Mega Man.

 

Karama:Help out yuska.

 

Gundam force:Protect earth.