Episodes 7-9 of the Soukyuu no Fafner: Dead Aggressor - The Beyond series.

In the year 2061 AD, Japan has lost its sovereignty. The Japanese people spend their days as oppressed citizens after being divided and ruled by the four major trade factions. The country became the forefront of the world following the deployment of AMAIM—a humanoid special mobile weapon—by each economic bloc. One day, Amou Shiiba, a boy who loves machines, meets Gai, an autonomous thinking A.I. The encounter leads Amou to cast himself into the battle to reclaim Japan, piloting the AMAIM Kenbu that he built himself.

The story takes place in a time when the world is in the pits of despair after being ravaged by a poison called "shinobi" that came to earth via an asteroid. The people run away to the place called "Kairiku," a place that used to be the bottom of the ocean. Here, the people try and protect themselves against the effects of the poison. In such a world, there was a single light of hope. The "Holy Weapon Giga Road" and the legendary warrior "Yagyuu" are needed in order to counter the effects of the poison. In order to save the world, Ame, a princess of a fallen nation, stands up in order to save the world. (Source: ANN)

Back on Sonic's home planet, Eggman has collected all 7 of the Chaos Emeralds, and is about to have absolute power when Sonic interferes, causing an explosion that sends everyone from their world to Earth. Sonic and his friends team up with 12 year old Christopher Thorndyke to collect all the Chaos Emeralds and defeat the evil Dr. Eggman. (Source: ANN)