I wish they would have introduced her earlier on in the season. I would have loved more of a backstory with her. I haven’t read the manga, but I assume there is more to her there. I have seen some of the character sheets that have been produced though.
Izutsumi becomes a full member of the party, and will run with Laios and the gang for the foreseeable future.
We’ve already gotten deeper dives into Marcy and Senshi. Rest assured the same will happen for the rest of the cast.
Also, Kui is very open about Izu being the favorite character that she has created.
She has commented many times about how anxious she was when waiting to get to introduce her into the story.