Come to think of it, DMM got some marketing strategies on them. You can fully F2P without problems. But if you want to whale, You either wait for deal or buy loads of gems which is expensive. And if you have some spare pocket money, you will want to support them once in a while anyway for their great services. Not to mentioned that permanent reissued must be one of the greatest things I ever see in not so many browser games I played since no matter how much you start late, you'll never feel left out and can reach adequate level to challenge harder content eventually.