As far as I'm aware, even if you meet the requirements for this achievement Iori(Ura) and Leona(Ura) are not guaranteed to show, as Rugal can show instead. Below are the requirements:
To have these characters appear, you will need to have between 6 and 9 DM's or SDM's, as well you cannot lose a single round before the fourth battle.
So again, pick a character that you're good with and make sure that you meet the criteria. If Rugal shows up instead, curse at him and restart your game.
Note: To make these easier, make sure that you do the following in the Options menu:
Set the difficulty to 1 (Easiest)
Set your players power gauge to MAX
Set your defence to level 8
Set CPU's defence to level 1