So I don't know if I would consider her a Monster Girl, but more like a cannibal of sorts. She mentions loving Japan and how tasty the "meat" is and she tells him he'll live on insider of her. Lastly, on the first page she is carrying the suitcase with one hand, but on the last page she needs both hands to carry it. Obviously a great deal of weight has been put in. That's my two cents.
Actually Succubus does have it's own tag. I can agree with you, since when I see that tag I typically expect something a little more....outrageous? It's hard to gauge sometimes because you might have a story that involves a snake god turning into a lady or something like that. Would that be still be considered Monster Girl (It's still tagged that way).
This was filled with so much love, care and devotion. Not a single panel wasted and each page was filled to the brim with the artist. Their use of shadowing and line-work almost gave it color. It was 58 pages of amazing and I would have love to see the ending panel in color, just to add to every little thing