SHE IS JUST NOT IT!!1!1!!!!2!1!!
THE FIRST FEW SENTENCES ALREADY SAYS WHO;
"I found someone stronger." "I knew you're the right one for this job~" or something I DON'T KNOW.BOOK IS NOT STRONG. BOOK IS WAY TOO FUCKED UP TO DO SHIT LIKE THIS. ALL SHE DO IS ALL TALK AND NO SHOTS. THERE I SAID IT.
BUBBLE IS THE CLEAR VESSEL. Who was way stronger than Pin and managed to get rid of her? BUBBLE. Who is careful with their steps because they know it'll be their death if they mess up? BUBBLE. Who had an innocent mind and doesn't want to hurt anyone in a bad way like Grassy? BUBBLE.
Book is just too angry with shits and focused more on Ruby and Flower too much. How and why would she be the vessel when she already got problems of her own? I know she looks suspicious with the disappearances of her, but when was it? When she's off buying groceries, ingredients for a cake, IN BROAD DAYLIGHT. She is NOT plotting ANYTHING.
Meanwhile, Bubble already had a problem when she first got back. She doesn't want to be a hero to them. She has a huge strength increase. And a more kind and soft attitude around Fanny. Of course she wants a list of people to kill first.
Conclusion, Book is not the Vessel, Bubble is. Even if it's way too cliche, I'LL STAND MY GROUND.
And if I ever get this wrong, I'll do a voice over from one of the FG2 chapters.