I've been having the same problem with the strong Kasumi's, though I do think that Naraku is being fair for the most part. Even though I get the really strong ones, I still get the weaker ones as well. Sorta random unfortunately. I've tried using elixirs to get rid of them and try my luck at a new one, but the strong ones just keep appearing. Tried three times in a row and kept getting the 8 million one so I've decided to stop wasting money. I just find it a bit annoying that my rank keeps going up slowly. *Sighs*