These comics take the route that shipgirls are spirits manifesting inside humans as opposed to being summoned out of nowhere.
... Arata...'My' name is Asano Arata.And your name is Yoshitake Makoto, right?You are a human being, you're Yoshitake MakotoSo without a single doubtNo matter what you remember, you are a human beingIf you're about to forget, then I will always call out to you