If you're being serious rank is not the same as level. Only Xyz monsters have rank, just play a deck that can summon level 4 monsters and use Yuma starting skill then add the free Zubaba general in your Ex deck.
Zexal's World Stages
There are only 30 Zexal's World Stages. Well, here are all Stage Missions and rewards:
Nah, just use 10-15 Level 1-4 monsters with 2k DEF and the rest tribute monsters with even higher DEF. Then, play against a Level 10 NPC and set your monsters one after another. They will always attack you and you easily win in their turn.
On Stage 6 it says " use rank 4 or higher monster cards 2 times in one duel world zexal duel", does that mean to use 2 monster cards with 4 or more stars in a single duel because i did that but it does not count