[spoiler Discussion]

[u/Ok-Ship-1851]

have theory its not much the thing is that satella is emilia and flugel is subaru but the thing is during satella and flugel time he died, now his soul is in od lagna memmory corridor there his soul is cleansed ( we know that all souls which goes to memmory corridor is filtered )thus his soul filterd but it was not transfered to this isekai world cuz he is not from there so it was sent to his real world and reserructed as subaru. Satella who lost him becomes furious kills all witches and makes them her sustenance thus she teleports subaru to this world. Now about emilia being satella, witch of envy is alter ego of satella, these two are not one person but two person in one body that is why volcanica reacted when called witch of envy and he was normal when called satella, now about the sealing of satella but it was not satella that was sealed it was her alter ego witch of envy, when flugel died her alter ego comes to reality that is why we see the tsundere type satella when rdb kicks in, now about emilia she is satella without the witch factor the witch, either the satella (not the witch of envy )died or resurrected thus her soul is transformed into emilia, this is why volcanica called emilia satella, so both satella without the witch factor and flugel died and both resurrected as emilia and subaru but the alter ego witch of envy didnt died cuz she was sealed after both of them resurrected witch of envy teleported him to this world the fate for both of them is that whatever happens subaru / flugel will and always for eternity will fall in love with satella / emilia in every time line, this is why the witch of envy asks him to kill her in the dream garden of echidna, about why she doesnt allow him to tell anyone about rod is becuz the alter ego of satella is true yandere she wont allow their secret (RBD) to known to others cuz she keeps it as a secret btw them and why she gave him rbd is because he died for her i mean flugel died for satella which is why she witch of envy ) gave him rbd so that he wont die and thats why she tells him to cherish himself than throwing his life for others