Ame-chan is a very small goddess, cast into Gensokyo from parts unknown. For reasons unknown, she has been driven out of her mind, and is basically a tiny little ball of jingoism and madness who seeks merriment and happiness, usually at others' expense. Despite this, she's too small and has no control over her powers, so she isn't much of a threat, but due to being a goddess she cannot be killed and would be exceedingly difficult to seal. Finding out about her origins and why she's so nuts will be it's own story arc.