I would take Alisa in the Edge, the last dungeon of Phantasy Star IV : as she was the first heroine of the serie, that's for me a logical choice ! The first heroine to see the end of the serie is highly logical
And to help finish with the Profound Darkness as ancient queen of all Algo
And as level thirty is the max you can reach in the original on Master System : that would be so great ! With her legendary Laconian shield and sword !