Rereading this, to remember the story at all, I can't help but wonder if the little sister isn't some kind of construct arranged by the administrator to monitor Reito. After all, he couldn't return to his original world, probably due to sacrificing himself for the sake of his friends, so he's now in another game world. Assuming anyone even was trapped anywhere in the first place. Maybe the players just got their consciousnesses copied and thus the (digital) copies blisfully believed they are living humans trapped in a game. But who knows. This is a bottom of the barrel level isekai, so one shouldn't try to analyse it too deeply.
