if you just started playing this game (or not)
try getting Rainbow diamonds as much as possible and saving it, such as doing Challenge battles, League Battle, Quests and Solo Mode
(it's recommended to finish solo mode since you get around 800+ RDS from it)
then repeat the process until you have enough RDS to start pulling on your favorite EX banner and pray you get one.
Always remember to claim your free daily RDS.

( THE ONE PIECE IS REAL!!!!!!!!! )

(it's easier to reroll on mobile version than Steam version cuz Steam version won't allow you to make fresh start so you're stuck with the account you just started with)
You can now Reroll on steam by opening the setting while in start menu

1. Open your File Manager and go to Android/Data and rename com.bandainamcoent.opbrww file to anything

2. Clear OPBR data then rename the file back to com.bandainamcoent.opbrww

3. Open OPBR and you're now start with a fresh account

(DON'T OPEN THE GAME BEFORE YOU DO THE STEP 2 CUZ YOU WILL NEED TO DOWNLOAD INGAME DATA AGAIN)
you can repeat this process many times and it's very time consuming unless you're lucky enough to get the EX char earlier

now for the fastest way to get EX char is to...... spend your money of course.... (they are overpriced)

You can purchase a limited time banner that guaranteed random old EX Char
(there's EX char that are good due to buffs they got such as Gol D. Roger)

or

purchase a ticket for EX Char that are currently available in the Gacha


(good luck getting EX char with this one)

this game sucks