Mizu is pretty awesome, though I've got a few gripes.
- No difficulties, always good to have at least two difficulties. Some people could have a really hard time with your script, or find it a walk in the park, so be sure to split it up a bit.
- Color scheme. The Rainbow danmaku would look so much better without the use of White. Could also be more structured, instead of the randomy-look it has now.
- Time between spellcards/attacks. Put a little delay between each attack (something like 2 seconds), to give the player a bit of a breather or to at least move into position. Unless you want the player to feel really cramped or rushed.
Otherwise this is a pretty fun script, it has some nice danmaku in it, despite it being so short.