Games : is Ereshkigal a Last One?

I unlocked the Ultimate Lair and defeated every Last One in it with the exception to Ereshkigal.

Now i still had a few hours before the final battle so i figured iu head back to the Oasis Lighthouse and submit my completion of "Last One Standing" now that i had killed every Last One without having to deal with hunting them down myself.

I confirmed in the Bestiary that all the monsters were extinct with the exception to some and made sure to tavel each floor one by one to ensure they were all cleared but i couldn't complete the quest. so i am wondering is if Ereshkigal counts as a Last One, if not then what am i missing?