Chime
"HEY, listen!"
I agree, personally I thought the isekai aspect was too played up. I like how in this manga, her past self is a much more like a vague memory than actually constantly active!y interacting with her with that annoying chime sound, as if she had Navi from Ocarina of Time with her or something.
Were it not for a few hints otherwise, I wouldn't even have been sure in the manga that her past life was necessarily from our world...it could almost just as well been an in-world reincarnation. Almost..there are some fairly obvious clues, otoh. But yeah, it's more subtle. I feel it would have been just fine as a regular fantasy without the other self entirely, other than her being a bit too knowledgeable for her age.
I feel like the anime isekai voice in her head is over-exposition and dumbing the story down; it robs Sora of much of the sense of her own personal agency, and also just makes the whole thing feel more cliched somehow. Overall the whole thing just doesn't reaonate for me like the manga does and feels rather twee, even.