See Reimu, you could've been Marisas Luigi and had ...those... as well.

Careful there, those things aren't permanent.

Break bricks while you can!

I don't know if Reimu got envy or is just scared...

Deciding area of attack

I'd imagine Marisa would say at one point, "What was that, Reimu? I couldn't hear you over the sound of my tits"

StriderTuna said:
I'd imagine Marisa would say at one point, "What was that, Reimu? I couldn't hear you over the sound of my tits"

So that's the reason why the BG music changed when she is in that form...