I think Big Mom might be a Homie or at least “possessed” in some fashion.
In Chapter 1013, where Zeus was about to be eaten by Hera, he escaped, clinging onto life by being led onto and possessing the Climatic Tact?
The constructs created by the Soul Soul fruit can eat each other to gain strength, while the more dominant Homie takes the power of the Homie consumed.
So using that same logic, I would propose the same is true for when Big Mom ate Mother Caramel. However, there probably are some special allowances for the fruit user themselves as opposed to a construct. Therefore, when Mother Caramel was eaten and died, her soul might have been melded with Big Mom’s upon Big Mom gaining the ability.
Other pieces of evidence that might suggest that Mother Caramel’s personality might have a reflection on how Big Mom has acted through us the readers, knowing her, here is a two-fold explanation.
1: Souls retain personalities:
We saw this in some of the Homies Big Mom made from her soul. However, we see this as a factor of the One Piece World through Law’s ability to swap the souls of other people, as he did on Punk Hazard. Furthermore, we know that Devil Fruit’s abilities are attached to one’s body, not their soul. Thus, while the Devil Fruit might give clearances to the soul such as astral projection or soul-self extraction, the fruit itself is a body-bond ability. Again, we see this with Brook, he had to return to his body when he died.
2: O-Lin exists:
When Big Mom hit her head when her ship was capsized, she reverted to the persona she had as a little girl. Why is that? Well, that’s when she ate the fruit/Mother Caramel, so likely that’s the real her coming to the forefront without any influence from Mother Carmel. So whatever soul bonding or soul preservation Mother Caramel did while within Big Mom back in the day can be undone temporarily by physical trauma.
Additionally, Big Mom’s end goal, while not evil, does parallel with Mother Caramel’s dealings:
– Mother Caramel groomed orphaned children with promise and sold them off to the Marines.
– Big Mom has made children and has groomed them into her militia.
Personality-wise even though there are many missing years, but there does seem to be a difference before Big Mom ate Mother Caramel and after.
– Mother Caramel had multiple sides to her personality.
– Big Mom originally was good-hearted with fits of rage. It was only after obtaining her fruit that we see her have such a wild and multi-faceted personality.
Of her personal weaponized Homies, Zeus, Hera, Prometheus, and Napoleon, I would say only Zeus reflects Big Mom’s true self. Zeus has been shown to be a naïve child that responds well to being fed and treated nicely but is mainly incompetent and only listens to Big Mom out of fear, not loyalty.
Napoleon is what Big Mom currently is; he has several modes and changes in demeanor depending on those modes. However, unlike the others, he will not act unless called upon by Big Mom. Prometheus is a mixture of Big Mom’s primal rage and Mother Caramel’s cunning, fitting as the first Homie we see Mother Caramel created is just a little sun named Pandora. Finally, Hera seems to mix with Mother Carmel’s lady-like persona of a nun using honorifics to address Zeus, while possessing Big Mom’s gluttony has she had no qualms with eating Zeus for power.
So break down; what do I think has happened here?
Well, I think upon being eaten, Mother Caramel imbued a set number of years of her lifespan into Big Mom, tying her soul to hers. This bonding perhaps has had long-term effects over time but can be undone temporarily by physical trauma. Then when Mother Caramel’s body was digested, Big Mom gained the abilities of the Soul Soul fruit proper.
Theory by orbman77 (https://www.reddit.com/user/orbman77)