In episode 6, we learn that
is the woman Rimuru is destined to be with. She shows up in the next episode.
She also dies a couple of episodes later, the next day in-universe. Aside from her showing up in the OP and ED, and being a quest-giver (for Rimuru to be a teacher) several episodes later, she doesn't have much going on in the series.
Why is she considered so important and "Rimuru's destiny"? Why is she seemingly more important than Veldora, the ogre women, Miliam, etc?
Why is she more important than any of the other monsters/spirits that Rimuru absorbed?
I'm only familiar with the anime, so if the manga/LN goes that much more in detail about this, then don't spoil it and leave the answer somewhat vague.