Start debugging with logging on dev and on production.
Simple example:
import logging
...
logging.info(entity.property)
Your problem is that you are not providing a key_name/id for the entity you are saving (if everything else is fine), thus when you try to display it you get nothing.
Change you save logic to this:
def post(self):
content = json.loads(self.request.body).get('content')
entity = ndb.Key(Storage, 'name').get()
if not entity:
entity = Storage(id='name', content='') # see here
entity.content = content
entity.put()
or as an alternative:
def post(self):
content = json.loads(self.request.body).get('content')
entity = Storage.get_or_insert('name')
entity.content = content
entity.put()
If you need an example check "How to use GAE with AJAX" from a previous answer and this is the repo