World ends with you - Shiki day 7 help

I know this one's kinda old but somehow I can never get the star for shiki day 7 "replay"One of the things to do is "defeat noise number 91 at hard or above"
I went down to the place to find the blue noise, defeated it at hard... no star. Went back to do it several times, still no star... I even went back to defeat it at ultimate level and still the star in the chapters page didn't light up. I wonder what I'm doing wrong? Has anyone else experienced the same thing?

Maybe there's something else that you haven't done.

hm? like?
I've completed all the other quests on the same day =\

Well maybe you have to kill two of them.
Try looking for a guide at Gamefaqs
That could possibly help.

hmm I actually did kill two of them at one time
it still didn't work thoughI've looked through google and all I get is where to find it and stuff like that

Replying to #5

But the noise is a boss.
Look here
http://twewy.wikia.com/wiki/Noise_List

yup that's the one i killed
the "post game blue noise"

Try starting the mission on hard.
So don't make it on hard just before the boss.

thanks for your help
it's been on hard the whole time T^T