Z Mind 1
But as if that weren't hard enough, the Earth comes under attack by an alien force.  In the grand tradition of Giant Robot anime, the mysterious giant robot Z-Mind (and it's component robots Z-1, Z-2, and Z-3) is all that stands between Earth and total devastation.  And the pilots?  Of course, they're the three older sisters.  Untrained and uncertain, the three sisters will have to make it up as they go along, but they soon find themselves making battle plans and shouting attack slogans like the most seasoned anime pilots.  But will it be enough?  Z-Formation!