Nagisa is a schoolgirl with schoolgirl tendencies, waking up late, rushing off to school and meeting up with friends upon the way. One morning Nagisa comes across a woman dressed in a strange uniform who seems to stare at her, unnerving Nagisa. Later that day, whilst staring out the window, Nagisa becomes aware of a ball bouncing by itself which flings itself towards her window seat, shattering the glass yet not harming her... Turning back to the front she finds a gaping mouth bristling with teeth inches from her face and no-one else about. She screams and the world returns to normal with her standing and the centre of curiosity of her class... why did she scream?

In deep space a battle wages between the forces of good and evil and the fate of the Earth hangs in the balance. The evil Neos Gold dispatches her invading forces towards Earth with only one aim: the total destruction of all mankind. Now it's up to Iczer 3 (the younger sister of Iczer 1) to defend the Earth from the deadly armada of Neos Gold, with only the Earth's single remaining battle cruiser on her side. But don't count her out; what Iczer 3 lacks in experience she makes up for in all-out enthusiasm.

[Source: MyAnimeList]

Iczelion, the final entry in the "Icz" series, is a departure from the previous storyline in most resepcts.

Throughout the galaxy, two villians destory and pillage anything in their path. Their names are Cross and Chaos, and they are ready to invade their next target: Earth. The only defense against these warriors are the Iczelions, a fusion of young girls, and Iczels, sentient body armor. Nagisa is a typical high school girl who is about to become the next Iczelion against her will, to defend the planet and save the human race! But not if she has anything to say about it...

[Source: AniDB]