There is some people saying that ch 11 final stage on hard mode is really hard, that you need lenna or yuna to complete the hp requirement. My first try was yesterday and it was really hard indeed, because the damage you took at the end of wave 2 also counts and it can't be healed at wave 3 because the game"reset" and at the start of wave 3 you take 5k+ hp damage. After many tries I could complete with lenna friend and sylph summon. Sylph wasn't needed on the video but it was just in case I miss some hp. I make sure to switch to lenna before taking hp damage, this way I can save some hp on the character that was replaced by lenna. On last wave replaced her with terra because of low skill charges that terra had.