In the mid-to-late game, you eliminate unneeded cards from your deck so you have multiple attacks every turn.
Same with Aquarius.
After a certain point having excess cards in your deck just slows down your attacks per turn.
Fierce and Aquarius allows you to rapidly reconfigure your deck chaining as well.
You can't chain Fierce star with anything since you will be losing warrior cards from your hand...
Aquarius is the best card in the game so I know that...
My point is why get Fierce Star when Leo is a better card...
It's easy to chain a bunch of warrior cards without having to get rid of any