So me and some people were staring at the screenshots and noticed some things...
Reimu and Marisa both seem to have their regular two options, as well as 3 extra options (note they're only at two power). Reimu's usual options are shooting cherry blossom-like things, while her extra options (what appear to be gaps) are shooting a forward focus type shot.
Reimu and Marisa both have yellow gauges in the lower left corner, while Aya has a blue one. The fact that Reimu and Marisa have different colors seems to imply that the color isn't character exclusive.
Maybe there's some sort of IN-like mechanic going on that changes your color from yellow to blue, with possibly additional colors?
All three also seem to have different symbols above their colored gauge. Oddly enough, Aya seems to have either a flower or a snowflake, despite seeming to represent Autumn (Reimu represents spring, Marisa's outfit shows she represents winter, Cirno is explicitly shown to represent Summer).
It's possible that the character's season can change depending on some mechanic, possibly the color gauge. As for what that season would do if that were true, it's still a total mystery.
As for some pure speculation, one guess is that the player has main options and a sub options, with the sub options changing what they do depending on your current season (which changes based on some gauge mechanic). Of course, that would definitely not be a "return to basics" or a simple mechanic of any sort.
