Luigi's Misadventures 5: Rougenia Merald's Challenge

PREVIOUSLY IN LUIGI'S MISADVENTURES 4:

Luigi defeated the Galactic Kids Next Door and its supreme leader Numbuh 1 and bring peace to the universe.

Luigi and Rike returned to their world, but their spaceship was ambushed by bullet killers. Luigi and Rike tried to escape, but their spaceship was hit and crashed in Megaville.

Luigi and Rike survived but their spaceship was severely damaged. They discovered that Megaville is being attacked by the same robots used by Merla. But how? And why?

Luigi needs to find where these robots came from and who is the mastermind behind the city siege.