You can buy some characters outright, but MANY are given to the player as they progress.
I haven't really felt the need to spend money on anything, but have paid for a few items to make things more convenient. Definetly not p2w.
Some characters are given after checking in so many days in a row. 15 days for the first, generally 30 afterwards. I missed a day here and there and I paid a small crystal penalty and all was forgiven, no progress lost.
The story, while typical, is enjoyable. The characters all interact in their own way, fulfilling most of the typical rpg tropes. Although this may seem like it might be dull, I would advise caution in writing off a well thought out story.
My interest in this game has been consistently curious. Ive probably downloaded and deleted 12 - 20 other games in the two months I have been casually playing this title. It has never been my main, but I havent ever considered deleting it.