This would be fun..
Tenchi Masaki: Tenchi Muyo
Sephiroth: FFVII
Kagato: Tenchi Muyo
Goku: DBZ
Jubei: Ninja Scroll
Gendo Ikari: Evangelion
Kaname Chidori: Full Metal Panic
I can see it now...Goku chasing Tenchi around demanding a fight against such a powerful opponent; Jubei and Sephiroth testing eachother`s sword skills, Kagato and Gendo arguing over who had the more evil and demented plans, and of course Asuka and Kaname probably beating the crap out of eachother(can we say personality conflicts?)