As I said the incest part is not only for MC, don't worry I didn't put this tag for clickbait.
Also, Alice is not a MC childhood friend but something strictly identical to sister (And you will never see MC talk about her with words related to friendship). In French we call these people "
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" (or "Soeur de coeur" for sisters) wich means "A person whom you consider to be your brother/sister without having a biological link with him/her".
Unfortunately I didn't found a word or expression in english for this french term, translators say "heart brother" but it seems nobody know this term on the internet, and soulmate is another thing radically different.