Elegant Impermanence of Sakura/Gameplay
The game features a system where enemies can be "dyed" colors. Enemies can be colorless, green, blue, or red, indicated by the small animated swirling texture on small fry and by the aura, for large fairies. Killing large fairies dyes small fry around them that large fairy's color (there are only red and blue large fairies). If a small fry already has a color, dyeing it again will succeed, but will also immediately kill it (known has double-dyeing). Additionally, double-dying 3 or more enemies at a time increases your PIV and chain combo in the HUD, the latter being necessary to unlock last spells.
Colorless and green-dyed enemies drop items to fill your bombs, red-dyed enemies drop items to fill lives, and blue enemies drop point items (which also fill your bombs). Killing undyed or green enemies produces large amounts of revenge bullets on higher difficulties, so you're highly encouraged to dye things before killing them.
For all intents and purposes, colorless and green are identical, except that green enemies die immediately when dyed since they already have a color.