I'm probably wrong, but since earlier there was discussion of the house being gone and the sentences you quote are right after 太郎さん found out he had been gone 100 years and lost everything, the には was pointing out that where he is now, in comparison with being in 竜宮城, he has no home, no mother, nothing... But that's probably just my overly poetic way of looking at things.
EDIT: i wrote this while Mike answered. I understand now, thanks Mike. I was definitely overthinking it.