I think that the evolution family is so pointless, personally.
And NU is part of a rating system that competitive Pokemon players use to tell which Pokemon are good, and which aren't. NU stands for "Never Used," and is the lowest official rating of a Pokemon.
Manaphy is Uber, which means the best of the best. Kyogre, Groudon, Deoxys, and other legendary Pokemon also have this rating.