I'm sure this function is not even rigged... just a series of bad luck imo. I have spent enough coins to get a quick rune and a half to finally obtain a red chakra. I'm sure that my account is blessed with misfortunate and I will never get lucky on that account as I even spent 240 seals and not get Naruto Sage Mode in the Sage Treasures and my F2P accounts gets Naruto in the first rare pull and red chakra in under 5 mil. So yeah its RNG from there.