Just Started!

If you're looking at Babel strategies or the Sealed Battle rankings, there are several must-have characters. Right now, I'd recommend limited anniversary characters like Sonata, the exchangeable School Festival Problem, and Canon, who's planned for November. Characters with limited acquisition methods are generally good to have. For permanent characters, something like Accident Orlas comes to mind... As for firepower, you can make it work with enough training. If you're only interested in the story, prioritizing your favorite character's growth is perfectly fine!

This year's anniversary-exclusive mileage can be used until mid-November for Canon (common). Mileage accumulated from gacha pulls for non-anniversary exclusive characters & scripts is common and has no time limit. You can save up mileage by pulling gacha when you have spare gems, and then use it to exchange for characters you really want. Anniversary-exclusive mileage will automatically convert into tickets exchangeable for training items after the period ends, so if you have 240 (or 120), it's better to use them up.