In a way are Callisto and Eve the same person?

Yes. I'd say they are.

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The way I look at how reincarnation works in the Xenaverse is how I look at some reboot series'. Some reboot series' ironically have new stories & a new identity, but still retain some elements of the original series. That's how I look at Annie for a random example. In her new rebooted life she had a new personality, new interests, hobbies, etc. Maybe there were times in her life here or there where she acted a bit goofy (& that was perhaps her unintentionally acting upon elements of her original soul, Joxer), but for the most part she was always being authentic to the new identity/personality of her soul/new life which was completely different to how it was in her previous life.

I feel like the dormant memories of her past life within her soul were becoming more awakened in her adult life, and that's why at the beginning of "Deja Vu All Over Again" she was acting more Joxer-like. I genuinely don't think that Annie was acting all Joxer-like her entire life. If anything growing up she probably had a personality much similar to Minya's (especially the fangirl part).

It's subtle (or not so subtle depending on how you look at it), but the Joxer-like nature of the "subconscious mind" of Annie's soul was practically breaking out to the surface all throughout the episode "Deja Vu All Over Again" before it was revealed that Annie was Joxer in her past life. Once Annie had finally accepted it & fully embraced it I feel like her 2 selves (the new personality her soul has in this life & her old personality from her past life) became 1.