Elk and Tsukasa
Well this topic has been heard of a lot,the funny thing about Tsukasa and Elk is that they both act a like, they both hang around a cat-like person, and three;they both are Wavemasters.Now pretty much,people think that Elk is Tsukasa and vica-versa.There really isnt much to clear up with this confusion,Tsukasa has grey hair and brown clothes and Elk has light blue hair and blue clothes.Also their face markings are diffrerent.Now if you cant tell the difference between the Tsukasa and Elk,then you must be freakin' blind!

Orca and Bear
Here are the comparisons,they both are blademasters,they both have the same type of personality,and they both have that Braveheart thing going on.Orca's face is green and white,and Bear's is blue and brown.
Blackrose and Mimiru
This is the same that goes with the Tsukasa and Elk thing.Here are the comparisons,they both are heavy blade users,they both have the same type of personality,and they both have tanned skin and the yellow markings on their faces.Blackrose's hair is pink,and Mimiru's is brown.Plus,in .hack//mutation you meat Mimuru and I had Blackrose in my party.

Natsume and A-20
Here are the comparisons,they both are twin-blade users,they both have the same type of personality,and they both have fox-eyes.Natsume's hair is green,and A-20's is redish-brown.Plus,in .hack//mutation you meat a-20 and I had Natsume in my party.