Is the game free-to-play or pay-to-win?

As of this writing, the only microtransactions in the game involve items that you'll need to use the Wish (gacha) system. Almost the entirety of the game is accessible for free, albeit time-restricted or by schedule. Of course your life will be a lot easier if you're lucky enough to draw powerful, high-tier characters and multiple copies of 3* or above weapons but aside from that, free-to-play players can enjoy the game at their own pace.