Aria the Natural: Sono Futatabi Deaeru Kiseki ni...

This is just a 5 minute episode that serves as a quick introduction to the series. It helps provide a mental catch up if you took time between The Animation and The Natural and as such, people consider it episode 0. There's nothing else to really review besides the fact that the OP/ED of The Animation is stellar as always. Unfortunately MAL requires a set number of words written for reviews, as such, as an extension of both seasons - I would definitely recommend watching this series at a slow pace. The episodes structures are designed similar to one another in order to create a senseof familiar comfort, one that could easily become 'boring' and 'tedious' if being watched back to back. As for bridging the seasons, I think that while The Natural had one too many mysterious and other worldly elements injected, the introduction of actual character progression really helps provide the hook the first season lacked. Amanchu! examines this character growth/struggle in greater depth, so I would also highly recommend that if you have not already watched it.