I'm of the opinion that Japanese names are corny if used unaltered for Dark Eldar, as they are all too obviously Japanese, thus all too human. Archon Kojiro Kikadate might as well be Archon Cesar Dominguez, or Archon Yuri Umarov, or Archon Joseph Smith... If the Japanese is 'Dark Eldarised' (as you said you'd do anyway), Archon K'jirogh or some such, that's a whole lot better.
Still, I think 'Elven' names are a better start point. Do a Google search for Elven names, particularly Tolkien ones, choose one you like then twist it up good so it sounds like a Dark Eldar name.